Yes, a 48cm would fit well. I have a 54 Cervelo P4 and it fits without having to take off the rear derailler. The wheels attach with their supplied skewers so any size wheel from 700c on down would fit. Yes, accommodates aerobars well......don't have to adjust/loosen.....just loosen basebars and turn to side. Yes, I pack saddle and seatpost in the case in the provided pouch/bag. Basically you take off wheels......take off seatpost......take off pedals (which I pack in my tri-bag.....loosen basebar and turn.......thats it. It comes with built in padding but i bought extra foam to fit around the entire edge of bag and fill with bubblewrap and use foam pipe wrapping once the bike is tied in. Wheels to roll the case are protected and work well to transport. Has four easy open/close locks. Its probably the most expensive out there but I figure should be able to resell used if I need to. Bought mine from ProBikeKit.......who is still selling for just over $700 versus other places still trying to sell for $1400. There are reviews by BikeRadar and others on YouTube. I've transported 9 times with no problems....great case if you have the budget. Mine weighs 47 lbs when packed. Let me know if any other questions.