We spent a week at Yellowstone in 1999. Here is what I can remember as far as planning....
Make ressies early! We called a litle over a year in advance and and had to take our second choice for times.
Went late July..it was hot and dry!!!! Lots of people at popular spots, but found many trails that it was just us! Invest in good hiking shoes!!!
Stayed the first half in Old Faithful Inn...the west wing, geyser view...Beehive Geyser to be exact

. Rooms were just redone and beautiful. Connected to the main lodge but not as rustic. Had our own bathroom. no TV!!!!!



(main part of the lodge shared bathrooms) I think it was about $150/night. Absolutly beautiful!!!!!!
Second half we stayed in cabins at Mammoth Hot Springs. Not really rustic, sort of like hotel rooms, but free standing cabins. I think the price was about $80/night.
We usually packed a sandwich and snacks for lunches and ate somewhere along our travels. Breakfast we had in the room...usually quick cereal and muffin. No fridge, but kept milk in a cooler.
For dinner we went to Montana for pizza and did laundry, a few nights at the lodge, went to a cookout via covered wagon.
There is a lot to see. We bought a guide book before we went. Most days we had a small plan, but usually left the days wide open, as anything can change. For example, one morning we planned to hike a certain trail adn found it closed due to a frisky bear!!! One morning we woke the kids up at 4:30am, and hit the road before any tourists!!!!
Hope this helped a little. We had a wonderful time!
I could go on and on...PM if you need more info,
Karen