On handling divinations:
If it's a small part of the concept, i.e., you're going to throw the occasional Omen of Peril or Divination or Commune to answer some specific questions, then my groups haven't had much difficulty. Usually the player has a particular question in mind, and w/in the parameters of the spells they get an answer. Even though we could, of course, make hardcore nested conditional inquiries (a long string of if-then statements), we don't -- we all DM enough to know how hard it is to answer divinations intelligently.
If someone wants to make it a core element of their concept, one thing I've suggested is that it give them some spontaneous type ability. For example, if you cast the appropriate divinations maybe you can leave a spell slot or 2 free, as you "predicted" this would be useful in the future. I worked on a gypsy seer concept for someone and I allowed them to have a pool of random magic items available for this purpose -- but they weren't a full spellcaster.
Something like that is how other games deal w/ stuff like gadgets or characters like Batman who always seem to have the right tool for the job. You could even set up a system of "divination points" where the player can store them by casting the right spells (and using magic items, class abilities, etc.) and can then spend them as I described above.
All this should make the player feel like Divinations are useful w/out avoiding too many of the headaches.