Ignore him, do Jack's loyalty mission asap, you only need to worry when you complete Jack's and Miranda's missions. Jack's bonus ability (that you can train for yourself if you research it) is the best ammo power in the game. Warp ammo melts faces. Also, make sure you have everything you need done before you go after the Reaper IFF or bad things may happen when you try to do it after.

Tali is the only interesting female character in the game.

You can spend credits willy nilly, I was able to buy everything I needed but you may find it more useful to buy things that more directly relate to you.