Hi there Dan

Welcome to the forum good choice of entering this world

as you have probably seen from the various threads there are many options for chassis. some people (i have done this) dont bother with frames and uses the armour to form the chassis as well as protect the innereds. for your project HDPE is probs the best thing, as it can be screwed or secured with aluminimum angle pieces

drills are again a good choice

definitely go for a ready made esc option you will save yourself a lot of hassle, robot power or dimension engineering controllers are the best choice for a smaller budget

if you go for drills the robochallenge wheels are the best choice easier than anything else

i have some hdpe and some 75mm robochallenge wheels that i can sell on if your interested

once again welcome and enjoy the forum

alex