hi, i agree that looks very impressive,
ive only just finished my first ever robot (picture on profile) and ive got my wheels mounted in a similar way using box section and long bolts which i use as the axles.

i would say though getting each box sections hole and mounting it exactly inline for the other side of the axle, was a challenging thing 2 do, i had to ensure i made a hole exactly in the centre of the box section which didnt always happen so my wheels axles wernt straight so my drive belt kept falling off. I guess it could just be because im new to the robot sport and ive a lot 2 learn, but you could mount your axles on bearings which could just bolt straight down onto your base plate- they would end up being the same height and all you would have to then do is make sure they are inline which wouldnt be too dificult.

( the bearings im on about are this kind of thing http://www.technobots.co.uk/acatalog/Online_Catalogue_Cast_Pillow_Block_Bearings_380.ht mlhttp://www.technobots.co.uk/acatalog...Block_Bearings _380.html )

and as for making the holes in your base plate for the wheels drilling the 4 holes and grinding it out is the way i would do it but it would be better on some sort of milling machine but it depends on what youve got to work with. to make my robot all i had basically was a grinder, welder, drill and jigsaw- no proper workshop or anything.

putting a lot of weight at the back is good because if you managed to pick something up you would have a better chance of not tipping over and i do think you would need another ram one for crushing and the other for lifting, like storm 1 or a robot called craven from robotwars extreme 2

hopefully ive been a bit of help

calum