RE: That pesky rear footstrap
Sounds like you need a bit more time on the water, to get a bit more accustomed to what things feel like.
Are your footstraps in the full outboard and back postions, or are you running the rear straps inboard over the fin?
You don't want to be "lifting" your rear foot, but more "pushing across the top of the board", like you want to push the tail away from you.
As far as turning upwind, and constant fore and aft rig adjustments, I think you will find that when you are more relaxed in your harness and can "commit" to having the rig support your weight, the weight will come off your feet and go onto the rig.
This will help prevent catapaults, and let you use fin pressure to steer your board.
Push harder across the top of the fin to go upwind, and to "cant" your fin slightly to leeward at the top or root.
To go straight ahead, on a beam reach, ease off the fin pressure and hold your board very flat to the water (rail to rail or roll axis here).
To head off the wind, push a little with your front foot, tip your rig up (rake angle here) a tiny bit and your board will turn off the wind.
Perhaps some of your difficulty in "hanging onto" your sail is due to some boom height or harness line imbalance.
How high do you run your boom? Shoulder height? Chin height? Where?
Can you take both your hands off the boom momentarily?
If you do, does the rig simly stand in one place, supported by your harness lines, or does it fall forward or back? Does your sail sheet in or out?
Yes, you need to learn to "hang in the sail alone" and be comfortable and confident that the sail will support your entire weight.
When you get the feel for this, you can then convert all the power in the sail into forward drive to make you go faster, and it will take all the weight off your rear foot so it's easy to get into that rear footstrap.
You don't really need to "lift" your rear foot, just get the weight off it so you can move the foot easily into the footstrap.
Hope this helps,