Missed this thread, ill try answer some key points;

Lipo - ive gone of flightpower- delivery/customer support sucks, thunderpower seem consistantly good, id suggest buying through fastlad.co.uk, there really good, there other brands are also good.

Wheel grip- i used shore 50- 80mm od, 6 of them, all 25mm wide, with the magnet, other robots didnt stand much of a chance... i couldnt physically push it sidewards once it was on some steel sheet.

my gearbox's broke because i used bad quality gears, welding made them brittle, and the geometry was bad- tiny pinion on a large 2nd gear... the angle of the teeth just wore them out real fast...or just snaped the teeth off, gearbox's had no flex. Just bad design on my part.

motors;

Dewalt powerdrive kits - good in low gear, real powerful, but with an 80mm wheel it was a tad slow for my liking... but it could of driven all day long with the magnet in without getting hot, in high gear.... fire.

Speed 900's... would of been fine if the gearbox's were beefed up, with 9:1 on the 80mm wheels.... but with the magnet in.... more fire

If i was to do it all again and try to make the best fw pusher.... id probably look into sensored brushless.