From your post I would gather you are planning on racing with the SCTA/BNI with you sidecar outfit.
There are some minor rule differences between the BUB and SCTA/BNI rules. I think the 10% weight rule that SCTA/BNI has on the books is a very good move.........at the present time this rule is not part of the BUB sidecar rules, however, BUB does give you the option of using a passenger in the sidecar.
Regarding your question on ridged or suspension on the chair wheel........I would go for ridged, we have tryed suspension on some of our past outfits and found ridged is the safe way to go..........................
Best of luck....and welcome to the world of LSR sidecar racing........if we all can be of some help to you
fell free to ask...