Just a few thoughts- (my opinions and thoughts)
1) Deck height - older ones I have been around - 4' give or take a few inches - under 13'6" here to be legal
2) Empty weight - I operated one that was around 19,000 empty on single axle ( gas engine / steel hd deck)
3)Decking Steel = durable but not super friendly with steel tracks
Wood - I like better for steel tracks but have broken /cracked had to replace.
4) Air brakes (possible CDL license over 26,000 gvwr here)) cheaper to work on than older hydraulics -