The crowds aren't anything like YNP and actually we never noticed a problem on the west side. We stayed over there a couple of times and on the east side several times. The problem can be when will the Going to the Sun road be opened. That was delayed the last couple of times we were up there. You probably can't be sure it will be open before early July. Varies year to year of course. Weather is also a big question, nice sunny days seem to be at a minimum.
Glacier is absolutely a hiking park, meaning you have to get out and hike to see the park. Not that much to see other than the GTTS road.
Not much boondocking on the east side since that is mostly Indian Reservation. More on the west side but down south. Do not try Hungry Horse reservoir or at least be prepared not to find a space. It is very popular with the locals and was filled mid week when we checked. Lots of dispersed camping along Hwy 2 south of the park along the river that the highway follows.
On the west side do take a day trip up to Bowman Lake in the north, stop at the small cafe for their famous cinnamon buns. As for Canada go up on the east side to their Peace Park which is the northern boundary of Glacier.