can 2 ointments be applied at once?

these are the ones that have a 450 second duration…

Yea, you can apply as many as you want, they are unique buffs.

Generally your goal on most builds is to get yourself to sustained max resistances without them though, because you will want to have access to them to help out with certain enemies who can massively chunk your resistances like the nemesis Valderan, who can halve your Lightning resistance fairly easily.

On a related note, is there a way to see what buffs and conditions you have at the time?

They should just appear above your skill bar on the bottom of the screen. buffs on the left, debuffs on the right.