Waterproof shouldn't be a problem. Free standing is a real plus as there's not always enough dirt to stick a steak in and expect it to hold. Think in terms of size, height and ease. You can go pretty light if you can put your rain gear on laying down. The ability to sit up is always nice. Keeping your bag off the walls will keep you drier condensation wise. Two doors even if only one has a vestibule is helpful on dome styles depending on where the door is.

I'll suggest buying two or three completely different tents that look good to you. Set them up in your living room and try them out. Send whatever you like least back and try two more.

A lot depends on what a tent is for and what you feel you need to do 'indoors' over 8 days. Will a tent, for you or whomever, simply be a place to sleep, or is it a refuge from whatever or a place to hang out too? What other sort of camping trips might they be used for?