I’m not sure if they want in the front seat or back. However, if I get out of my car for some reason (look for a passenger around the corner is an example), then I open the door for them.
I do not inform them of surge pricing, however I often commiserate with them about it and explain it the way Uber explains it to us (attempt to encourage more drivers on the road). Because the pricing changes so much I never discuss actual prices with them, but do let them know they can get an estimate from the app.
I have a bag in my trunk, it isn’t big, has my personal things in it. Can still handle 2 or 3 suitcases in the trunk plus the 4 passengers. I’ve also had customers put musical instruments, boxes of work papers, and a bicycle in my trunk. Therefore I think it is good to have your trunk space be relatively clear.