So any Advice for playing on Hardcore and Insanity? I want to get my third S rank from this game.

Play the solder and Tech classes first. That way you have extra skills for the Insanity bionic playthrough...

Soldier with Singularity or Adept with Assault rifle will be your two best options. Having the bonuses you get from the "ally" achievements will really help also. The thing with hardcore and insanity is that enemies are just bullet sponges, nnot especially challenging. Just upgrade your assault rifle and singularity as fast as possible, those being your best tools.

Also keep in mind that the Mako has a scope which will really help with the vehicle combat- hold the left trigger then click the right stick.

I found the Engineer with the Assault rifle to be a fine choice for both Hardcore and Insanity.  Having both Decryption and Electronic as skills meant that I could take any combination of allies, not needing to be concerned that they had these abilities.  This let me take the teammates best suited for each situation. 

when your shields are down don't move from cover til they are back.   That's really the only trick to mass effect combat on any difficulty.

What is a good level to start on roughly, I have all the bonus talents unlocked.

I took my player once through the standard difficulty, maxing my XP (aka do all the side missions).  Then I took that same character through Hardcore, doing the same thing.  Finally I did Insanity, with a straight run through (no side missions), and got max level easily.  The whole experience was never that difficult, without any major sticking points.  Good luck.

Well, by the time you've played your character up to the highest level, you should be able to take down the enemies in Hardcore and Insanity pretty easily, but I'm not saying it's going to be fast. Lies is definitely right about them being bullet sponges. I suggest Soldier class with the Singularity bonus if you got that.

If you're doing this for fun, good on you. If you're just going through for the achievement though, do new game + with a previous character, and as long as you change the difficulty on the ship in the options, the achievement will still unlock.

Do a Barrel Roll! (Press Z or R twice)