500 x 500 is quite large for a FW.

Bitza was 450 x 320 and when we went to the UK champs we found we dwarfed most of the other bots! (besides Tron2/Seraph of course)

This is fine, but you'll find you'll suffer from the scaling factor and your robot will become very heavy very quickly.

Bigger base means more armour, more supports, more cabling etc.....