1) SOG is considered a deluxe and has some of the largest rooms on site. It's right across from the Poly, within walking distance if you want to use their transportation. It's not owned by WDW, so you can't get the dining plan and it's not decorated like a Disney resort.
2) should you stay there can only be decided by you, everyone has different likes and wants different things in a hotel room. Room rates are based on rank, check the shadesofgreen.org site to see what your granddaughter would pay. The buses don't run as frequently as Disney buses do, but you can always walk to Poly. Buses to TTC run more frequently, so you could always switch to a park bus there.
3) your granddaughter can buy tickets at SOG or, if she lives close to an active duty base, she can buy them there. Check the prices of the 4-day salute tickets that must be used by the end of Sept. and the prices of the Stars and Striped length of stay tickets. The Stars and Stripes tickets can only be bought at SOG.
4) nope, no Magical Express. You have to get yourself to the resort and back to the airport.
Personally, I'm not thrilled by the bus schedule. We always seem to just miss the one we want and the next one isn't coming for an hour. The food there isn't great either. I read recent reports that said it was pretty bad, but I haven't eaten there in at least 5 years so I can't say personally.
Check the website, they've got some great discount prices for various times of the year. My rank puts me in the 2nd pay tier and I'm paying $73 per night for Sept. Oh, they charge $5 per night to park your car and I don't think you get free parking in the parks if you drive anymore.