Once you upgrade your inventory size twice it doesn't feel annoying anymore. I also picked up dismantle early on so I could break down weapons I don't need immediately.I find myself backtracking to recycle shit far too often in this game...inventory management is one of the least fun mechanics in gaming IMO,
You can pick up Leverage 1 objects (like a coffee table), and throw them at Leverage 2 objects to knock them out of the way. I've done that a couple times to get past Leverage 2 boxes. It requires trial and error, as you kinda need to align yourself and the object at the correct angle to do it though.though there have been several places that I've come across that just sort of seem like you HAVE to have Leverage or some similar skill in order to get into an area, with no alternative route.
I agree with your post in general though, some of the upgrades you need to buy (like larger inventory) should have come default (or at least not be so expensive), and it would be nice if there were at least two ways into all rooms, you are correct in that there are a few rooms with only one way in (ie needing a specific skill). The game is still awesome so far with these minor issues though.
Some might think the huntress boltcaster weapon is useless, but it can be used to open doors by pressing the button which unlocks them. So for example, break a window on the side of the room and shoot the button. I heard also the bolts also bounce/reflect off goo so you don't even need a good angle on the buttton, though I've never tried it.