Agree about showing up early at Apgar early and seeing what opens up. There is constant turnover and it's first come first serve.
My wife made reservations for us out at Emery Bay campground on Hungry Horse reservoir. We stayed there the first night and then I got up early the next morning to drive the TV into Apgar. I got a great spot, paid my fee, and set up a tent and a couple chairs to show occupation, then I drove back out to Emery Bay and we had a nice breakfast and played in the water before hooking up and driving back to West Glacier. We ate a couple nights of National Forest campground fees, but it was not very much. We really enjoyed staying at Apgar and swimming/kayaking in the lake.
I will say that while I was setting up the placeholder tent I had a few people drive by and ask if I was leaving. By the time I was done it seemed like most of those who had been right behind me also looking for a spot had found one or arranged with someone who was leaving later to take theirs. FWIW
As for hikes and transportation, we took the shuttle one day to hike the Avalanche Lake hike, that was a nice hike with an 8 and 11 yo. We caught an early shuttle as it fills up fast.
For Logan Pass, we made a day trip (driving) and made a quick stop on our way to to St. Mary's. Parking is difficult most of the day, but found a spot and made a quick visit to the visitor's center and explored the grounds before having lunch and continuing on to St. Mary's. On the way back that evening it was still light, but the parking lot was nearly empty. We stopped and saw people hiking the Hidden Lake viewpoint trail, so grabbed our packs and made a fast hike up to the viewpoint and back. That was an awesome decision as we saw both sheep and goats on that hike that were right off the trail, but had to hoof it back to the car as it was starting to get dark (we were not the only ones out there though).
We did a couple other hikes, but those were the more memorable ones.
2019 Outdoors RV 21DBS
2016 Silverado 2500 Duramax
Equalizer 4-point WDH