Ciao, I'm at the point in the game now, where getting new milestones on the Crystalarium takes a VERY long time, I was wondering if it would be a good idea for now, to branch off into the other jobs, so I can get some easy HP and stats, or is it better to keep with the same one to max it out. I was wondering how you all decided to level up, and if you maybe know of any good guides that help out with the crystalarium? Cheers.

It completely depends on what kinds of character you are going to use and how you design their abilities together. 
I tried to lvl up one as commando/ravager, one as ravager/synergist and one as medic/ravager, which was the main usage for these characters. 
Eventually you're gonna level up your characters to a point where it matters more what items you equip and it's level than the chrystarium. Just lvl up for all you got and worry more about equipping the right stuff for your party.

You get more stats per CP if you stick to the main threads, except maybe picking up the first row or two.  Personally, apart from giving Hope a few points in Sab so I could triple Sab to make death-spam killing Adamantoises a bit easier, I didn't spend a point on any of the alternate paths until I finished the three primaries.

I stuck to the main paths, although I also upgraded Fang's sab role because I wanted somebody to cast haste (my fav. spell) in addition to being a sen.

Yeah I'm doing pretty much the same, I think I need to start grinding though, I reached Pulse, and some of the enemies are still a bit too strong for me, like the giant red tomato things. Where as everything else in the game so far I've been really comfortable with. I'll just keep grinding out the missions before I go on with the story.

Stick to the main paths until you reach pulse. then if you're feeling up to it, grind for 20 hours.

I would say to only focus on the other roles when you've already maxed out your current level of the Crystarium for the main 3 roles. It's also probably a good idea to only focus on one extra role at a time, to prevent spreading yourself too thin. It all depends on how much you feel like grinding, though.