Whatever you buy, make sure it has been regularly habitation checked (the tester issues a certificate to the owner much like an MOT but for safety of gas / electric / water / damp etc). LED lighting is a great benefit as it minimises the drain on the leisure battery when not hooked up to electic.
As said above, German brands are usually best. The vast majority are FWD Fiat Ducato. There are a few RWD Sprinter and Transits around but nowhere near as common. Don't be tempted by anything less than a 2.3 motor as it wont pull the dick off a chocolate moose. Mine is Fiat Ducato 130 Multijet with a 2.3 engine and tows nicely but you wouldn't want less.
The other thing to be aware of is that if you plan to use it for motorsport activities, you may find a rear garage or belly lockers useful for storage etc. This will however to an extent dictate the layout of the motorhome and may compromise your rear lounge wish.
The next major thing is to absolutely be certain that a towbar can be fitted. Some rear chassis are just extended with flimsy material and are unsafe to mount towbars on. Whilst on about towing, check and double check that the plated towing capacity is sufficient for a car and trailer. Some are plated as low as 800kg.
The payload is also important as this dictates the weight of the kit that you can carry in the motorhome before it is considered overloaded eg - the VIN plate will show a maximum gross weight and an unladen weight. the difference is the payload. Some motorhomes have stupidly low differences and wouldn't allow much kit to be taken onboard legally