Yeah I agree with the person who said that it's better to go with Assault and skill up the relevant "boring" skills to do with CPU, Reactor and Accumulator (as well as weapon skills, Basic Robotics and Nav obviously).
I was doing L2s in my Castel after a few days - extremely hairy, and took a while, but just about doable, after I died a few times and learnt the parameters. Now that I'm in my Assault bot after a couple of weeks, and can fit some tunings, everything's starting to flow nicely.
And for PvE at this level, armour is fine, I agree with the person above who says the armour in the game has a purpose and is not just for decoration; using armour, you still have to kite but you can be more relaxed about it and don't have to fiddle with targets so much.
Sometimes I use rep and hardener (either universal or specific), sometimes armour plate, and I've found plate to give the "safest" feeling against your weakest foe type, as the buffer is just so huge, and I can just about perma rep now (at least, it lasts until I complete a S&D or get bored gathering reactor plasmas), with maybe a few retreats. Specific hardener is also good when you know that the damage type is of a main type against those you are weak to (but sometimes you've got to be careful, as the mobs will use varied ammo types, e.g. chem, or against your weakness).
Mind you, all this is with Pelistal. I think I would pay much more attention to Accumulator with the other two races, but I don't think it would mean more than a few extra days training for comparable performance.