Be sure to get a reservation at a Beer Hall as they are not just walk-in.
I am not sure what this means. The tents at the fest? Beer Halls in the city?
But generally, for both, a group of two would not need reservations and for the fest tents, two cannot make a reservation, except maybe by overpaying for a "tour" that includes a seat in a tent.
The traditional beer halls in the city can get crowded, but I have often been able to find a seat, there are enough of them that you can easily find one that has room, do not be afraid to share a table.
For the fest tents, you are free to enter any tent, unless they have halted entry due to capacity. You can enter, walk around (well worth just walking through a few) and if there are seats available, that are not reserved for that time period, you can sit. Ask the staff in charge of each section, they know where the free seats are. Generally in the afternoon, during the week, you will have your pick of seats and tents. Evenings may be tougher, as more seats are reserved, and more people show up for the unreserved seats (All tents are required to have unreserved seats.) The weekend after you arrive will be a zoo, as it is closing weekend.
For places to stay, Freising is a nice town near the airport and on the S-Bahn line into Munich, 30 to 40 minutes to the heart of Munich. Erding is another nearby town on the S2 line, about the same time in. Just a bit further, but on a main line, is Augsburg, a pleasant city in it's own right, is 40 to 50 minutes by train. Each of these cities still have several places for $150 to $200/night. Hotels in Munich proper are very high cost.
I like to use Booking.com, they show a range of accommodations: chain hotels, small hotels, hostels, and apartments.