You'll be surprised, drill motors pack quite a serious punch, 4 of those and you'll have a very fast and powerful robot on your hands, people often use just 2. I'm not all that good with ESCs, but I am using 2 30a Electronize ESCs (cheap and cheerful), some love them, some hate them, I don't have any experience with others so I can't really give a real opinion, all I can say is they work good for me.

Steel ladder? I've never head of a ladder (I mean fullsize ladders) that isn't aluminium, some 2 step ones are steel, but aluminium is very very light, quite strong and I'm sure you can find an old ladder from somewhere. You'll have major problems using steel, it's a fantastic material but horrible to work with without the right tools. Lots of people on the forum do have the right tools, if you give precise measurements then I'm sure they'd be happy to cut you a piece or two.

Obviously you'll need a radio system, I'm using the Planet 5 2.4ghz transmitter/reciever set (quite cheap), I don't have much experience with others either but I can say it's been fantastic, and very very easy to set up so far.