If you're doing point to point hikes, you're missing out on a few good ones. More on that later. The good news is that yor time frame is perfect.
Not too many folks i know of have done Slide Lake but Squillax's group did so in 2004. I'm sure he'll chime in once he sees this.
If you want to do a four night trip a more exciting option might be to start at Goat haunt (you'll need to take the shuttle up to Waterton and then take the ferry down to Goat Haunt) and finish up at Swiftcurrent via the Ptarmigan tunnel. Easily doable in four nights: KOO, STO or MOL or GLF, COS, ELF. That would be my preference anyway. For three nights I'd stick with your plan but maybe swap COS for GAB. you can also det in an 8-mile dayhike to Helen lake from ELF, or even climb Bear Mtn. Point from Cosley before heading over to ELF.
Hike # 2 is one I had two permits for last summer---one at 3 nights and the other in 4--- and didn't get to go on either of them (long, sad story
) so i can't really comment on anything around Cut Bank. IMO, you'd have a more scenic hike if you got NON for a campsite. This way you get to traverse the 3 mile "skywalk" between Pitamakn and Dawson Passes. Begin at the St. mary Visitor Center,c amping at Red Eagle, Morningstar and Noname Lake. This is a fairly long 3-nighter but you should be fit from your first hike.
One other choice might be to do Gunsight Pass in a leisurely 3 nights staying at GUN, ELL, SPE. Or you could do GUN, SPE and SNY. Sperry has a few nice dayhike options and a killer view from the campsites
You shouldn't have any troubles utilizing the shuttles for any of these hikes and could probably get a room at either Swiftcurrent Motor Inn, Many Glacier Hotel or the Glacier park Lodge seeing as though you're going late in the season. Things start closing up a few days after Labor Day.
Let me know if you have any more questions.
So many mountains, so little time.