You should get a handbook when you pickup the car explaing pretty much everything.
On the scheme road tax is renewed by mb automatically and when it comes to servicing the dealer should contact you before it’s due to book it in. If you have any issues with the car contact the dealer and tell them you have a mb car. Some recently have started charging for loan cars but I never was ever charged.
Oh yeah you don’t have to pay any ap upfront, only if you added extras you might. Some try to get it upfront but again on the 4 cars i have had on the scheme I never been asked for it upfront.
also the car will be automatically be exempt from some toll charges or congetion charges like dart-charge or congestion charge others you may have to apply for.