Oh yes, the spec must include big wheels (five inches minimum, but bigger would be even better). Plus rubber tyres. Solid will do, but pneumatic would be better (just as long as you keep a pump handy)! Two wheels only need to be castors (and have brakes).
I would forget about stainless steel. A bright, plasticised paint finish would be my choice. For the library role, I would go for "baskets" rather than "flat top" tiers. Probably a deep one on top, and a shallow one below (for leads, papers etc
). I'm undecided about the buckets!