So I've beaten the game and am going back through to unlock all of the gates and that kind of stuff. I have 5 out of the six roles for Serah and Noel at 99 but they still feel underleveled. I need help just understanding maybe accessories more and which monsters are in the higher echelon. Right now I have a level 45 Flanitor as my medic, a level 40 Gremlin as my Ravager and I just got a level 20 Golden Chocobo Commando. Any info/suggestions would be great!

What do your stats look like? Also what weapons are you using. 
 
Some quick facts though if you want to know: Chichu is apparently the best Commando pet. You get him by throwing mog into the patch of flowers in front of the town in the Steppes. Cloudburst is considered the best ravager (can get close to 1200 magic at max level) and is found in the southern trenches of the Steppes during cloudy weather. Flan and Green chocobo seem to be the most effective healers, Green chocobo gets better stats and spells, but Flan's feral link basically heals everyone to full HP which I believe is better than whatever the chocobo has. However Flan has very low HP so you will just have to pick if you value his feral link more than the chocobo's increased stats.
 
You may of been in that group that messed up your stats a bit, but you will be fine doing any endgame stuff. For accessories I would get the Kaiser Knuckles for Noel and the magic equivalent for Serah (I think it's Magic Crest but I can't remember the name for sure atm). Then through crafting  you can get another small accessory to give them some sort of attack or magic boost. Your key goal should be raising their Attack and Magic as high as possible, and then picking an ultimate weapon you feel comfortable using since you have quite a few choices.

I didn't even know you could mess up your stats, but of course that would happen to me! Also I saw a video where someone had a Twilight Odin which seems like it would be really good but maybe not as good as this Chichu. Anyway my stats are Noel 552 strength, 434 magic, equipped with Vairadanda and 100 accessory capacity and Serah is at 428 strength, 632 magic, equipped with Izanami and 100 accessory capacity. I see much better weapons in the store but I don't know where to get some of the components like Trapezohedron or some of the weapons like Romulus and Remus. Sorry for the lack of knowledge but I hope you can help!

I'd recommend the Grimoire Hat on whoever you use as leader, it increases the effectiveness of potions. Your potions will heal a good amount and you can keep your party on an attack paradigm.
I've gone through the game with just three Power Wristbands on Noel. If you stack multiple accessories with the same or similar properties you can gain additional effects, with the three wristbands Noel absorbs regains 3% of the damage he deals out as HP. 
 
To get the Trapezohedron you need to beat a difficult boss called Yomi. He appears in the Archlyte Steppe after completing certain fragments, such as hunting boss monsters and finding all of the cactaur stones. The chief will give you the mission after a while.
 
In the Crystarium there are two types of nodes, large and small. Levelling a role on a large node grants you additional bonus stats depending on which role it was. Commando will give you strength, Ravager gives magic, etc. If you want you can min max, for example only levelling Noel's commando role on large nodes to get a larger strength stat. It's not necessary to finish any of the post game content though.
 
I used Apotamkin as my ravager, he's a little gremlin dude from 700AF. Flanitor is a pretty good healer, if his HP is lacking try and infuse him with a monster who has a Passive HP up skill. Chichu and Odin are both good, Chihu is a powerhouse and Odin has a lot of survivability. The game is pretty easy overall, if you can beat the final boss you shouldn't have too much trouble with the majority of monsters.

If its any help my setup is this...

Serah - Noel - Monster

COM - COM- RAV

RAV-RAV- COM

MED-MED-MED

SYN-SYN-SYN

RAV-RAV-RAV

SAB-SAB-MED

I've been using Yakashini for my monster SYN his Feral Link is godly. It instantly puts ALL buffs on all party members and charges fairly well. Been using a Blue Chocobo for my RAV I leveled him exclusively with Mana items and infused him with Zwerg Scandroid for Lighting Spells and Flanbanero for Fire Spells. He will naturally learn Aero and Blizzard spells. Lastly using Flaninator as MED leveled with a combination of items. I ended up just beating Raspatil who is by far one of the toughest enemies in the game with this setup.

Also protip if you don't know how to exploit this feature of the paradigm system. You can fill your ATB instantly every other turn if you swap to a new paradigm. For example the battle starts I fill up my ATB and attack. Next round I fill it up again after the last attack is cast switch immeditely to a new paradigm and your ATB will be instantly filled giving you a serious advantage. You'll then have to fill up your ATB once fully again then again on the next fillup after that switch and you'll have a instantly charged ATB again. This is CRUCIAL to exploting the limited stagger time you get for tougher enemies.

How to maximize your stats.

@Ross said:

I didn't even know you could mess up your stats, but of course that would happen to me! Also I saw a video where someone had a Twilight Odin which seems like it would be really good but maybe not as good as this Chichu. Anyway my stats are Noel 552 strength, 434 magic, equipped with Vairadanda and 100 accessory capacity and Serah is at 428 strength, 632 magic, equipped with Izanami and 100 accessory capacity. I see much better weapons in the store but I don't know where to get some of the components like Trapezohedron or some of the weapons like Romulus and Remus. Sorry for the lack of knowledge but I hope you can help!

Twilight Odin isn't that great, especially compared to Chichu (A good Chichu build can have over 1500 ATK). Cloudburst is pretty awesome though so I would definitely recommend getting and upgrading him. Bunkerbeast would be your best bet for Sen and Green Chocobo is probably the best Med. Just make good use of infusions.

As for weapons, you probably want to get Indrajit for Serah (ATB+50%) since she's mainly going to be a Rav so casting speed should be your priority (especially if you're going to use Tri-Disaster) and Odinblade for Noel since he's mainly going to be a Com. To get both Indrajit and Romulus and Remus (Noel's equivalent ATB+50% weapon), you need to farm Immortal.

I didn't know that the larger nodes gave you more stats of the class that you're leveling up...I feel like I just screwed up my entire playthrough lol now it is too late unless there is a magical respec option haha

@Zenaxzd: Really enjoyed the fight. Honestly not hard at all its just the wounding damage was really starting to build up which made the last few minutes a edge of the seat experience. I REALLY can not understate the usefullness of the SYN SYN SYN paradigm. Yakshini's feral link is amazing and a huge lifesaver. I'm trying to psyche myself up to do the Long Gui fight in the Steppes. I got worked pretty hard everytime I tried to kill one of those fuckers in XIII. So....still kinda nervous about that one. Is he any easier than in XIII?

How do Lightning and Amodar compare in terms of Chichu and Cloudburst?

@Ross: I've heard they are pretty decent but the fights to get them are pretty damn rough anyways. Lighting heals consantly and Amodar does really heavy damage. Unless you want them for novelty sake you have better statistical options avalible to you on the disc.

Does switching it to easy mode decrease the 7% chance to get Lightning and Amodar?

@Zenaxzd: I'm assuming a SEN/SEN/SEN is required? Because I tried to fight him without and even with full buffs he absolutely nuked Serah and my Chocobo. Noel, somehow survived even not being in a SEN role. Suggestions for SEN monsters?

There's an accessories that raises 40+ magic/strength and it also gives potion improvement. Instead of going to MED/MED which I find pretty slow since none of the character has curaga or better heal than curasa, I used potion and it gives better result than using those MED spell. It's also faster as well. Equipped Serah with it as she's only good to raise stagger meter and a good debuffer.