Yes, you can buy them at the ticket booth. Their "rule" is that you need to live more than 50 miles from a base with MWR/ITT, but I've only had someone fuss about that once (he thought it was a base within 50 miles of Disneyland, so he tried telling me I had to go to whatever base; I asked for a lead, and they explained the rule correctly).
It doesn't include MaxPass, but you can add MaxPass every morning (takes less than a minute). PhotoPass comes with MaxPass, though they also have a discounted PhotoPass if you have zero use for MaxPass and will be there for more than 4 days (breaking point in cost).
California does not charge tax on Disneyland tickets.
Remember there is a 6 ticket limit, and the qualifying service member/spouse must be present for the first use. And they *must* have their military ID to prove eligibility.
Oh, and as I always want to remind people, double check any ID expiration dates! Mine was expired by 2 weeks. That was an expensive lesson!