I haven't ever ported a saw...but have read quite a bit on it and I am about to try a saw soon...anyways, the ring should not catch as along as you are making the transitions smooth with no sharp edges or awkwardness. I wouldn't be touching the transfers for a mild porting besides just a lite smoothing. If you are gonna go without a base gasket, make sure you check the squish before you run it. .2 is very common. Anything under .17 is getting tight. As for raising the exhaust, it is usually not done because the reason you are leaving it out is for more compression and torque. Raising the exhaust puts you back to stock. However, i have read sometimes the exhaust needs to be raised to run optimally. Usually it is fine because you widened the port for flow.
I think you just left out the zero after your decimal point but I know what you were getting at; twenty thou. Returning the exhaust to stock height after having taken out the gasket will keep the same exhaust duration but because you have brought the head lower you will be compressing into a smaller volume (made the combustion chamber smaller) so you will still have a net increase in compression over stock but you are correct in saying that it will be less than it would with gasket removed without anything done to the exhaust port, so you are pretty close!
Because you will lower the intake port with the gasket removal, you increase intake duration which will be of no benefit if you deliberately create a shorter exhaust duration.( by lowering the jug and not at least restoring original port height).
The increased compression alone will yield a bit higher torque but it may well come in at a lower rpm than the stock saw and TW is correct in saying the max hp may well be lower than a stock saw because of what you have done to high rpm potential. It will grunt louder but it wont cut faster at least in medium or smaller wood.
Lowering the jug also effects transfer timing so you are leaving quite a bit on the table by not correcting it too. Work on the transfers is the most difficult part without the right tools especially on closed transfer cylinders. Simply making them bigger is not always the answer either especially on saws that depend on small base and high velocity transfers to get good scavenging.
There are a lot of different things at work in a two stroke engine and each thing or change to it affects other things, sometimes in opposite ways to what seems common sense. There
are ways of screwing things up and I have been hammered on in the past for pointing that out.