Battle bot mentorship

Alright GRM, I need help so that I can help my son. I've previously posted about my son's love of robots, and now we're taking another step. The plan to compete in the 3lbs plastic bot class. The event is in January:

http://www.angryroosterrobotics.com/p/rules.html?fbclid=IwAR3DqpLoh_DFf7yTR2gLlpeJSHQfd_KlCk7LijoAFJzdqs7mmtXPzep0qRM&m=1

I've got a sketch, some ideas on parts, thoughts on the type of plastic... But then it all falls apart after that. 

How much / thick plastic?

How much battery, how big motors?

Do I need to a speed controller?

I have a copy of Solidworks, how much should I invest in learning and using that versus just winging it?

Anyone want to help?

Here's the previous post from several years back...

https://grassrootsmotorsports.com/forum/off-topic-discussion/robotics-project/99256/page1/

I’m not sure how I could help, but sounds like a fun project. I’ll take a look at the rules tomorrow.