Game maker Tower Defense - HELP!

[lepape]

Hi,
I'm currently trying to make a TD game using Game maker, and well, I'm a total newb. There's tons of things I'm trying to figure out how to do, but there's mainly two questions I have, so I thought I might get some good help here.

First, about enemies. From what I understand, most TD games only have one object being used for every wave, it's just the sprite of the object that's being changed. That way, towers can always target "obj_enemy", for example. What I'd like to do would be to have many enemies with different behaviors. For example, one enemy would deflect all projectiles, another would spawn smaller enemies upon dying, etc. Should I use multiple enemy objects in this case, or should I add tons of variables on the same "obj_enemy" for all possible behaviors?

Also, I'm trying to use some grid system when building towers, so the tower would only move one square at a time when placing it. I tried to find info on how to do that, but I'm wondering if that's even possible in GM.

Thanks,