A few things: for 1998 the remote key - when the UNLOCK button is continuously pressed the windows & sunroof will open. LOCK button on remote will also close them. It get a bit more complicated- you really need an owners manual to make sure the key is in GLOBAL or SELECTIVE mode. But, the key does have that function.

In the trunk fuse box (maybe also hood fuse box) the top of the inside part of the plastic fuse box does contain a card listing all the devices that work of the fuse in their numbered location.

Cause of the mirror/window issue, could be wiring that passes through at the door hinge, are the door speakers working properly, and there is a heating element in the side mirrors that defrost - I'm curious if that is working.

The door lock is on a different system so if the door locks and unlocks by remote, that is no indicator of the electrical wiring to the widow and mirror.

Whole other issue, do a little research on the electronic key car came with two electronic keys and a third thin electronic key - they should all have metal emergency keys that slide out of their compartments in these three keys. The issue is Mercedes can only make five additional electronic keys for the car until a new black box has the be installed to allow additional keys to work - so make sure you get all the keys with the car and maybe even check the dealer to see how many additional keys have been made for the car.

I'm sure others will give better info on how to diagnose the window/mirror issue