Slab:
Best thing to do would be to go to a store that has a Sig in stock and play with it. Different folks have different sized hands, so what works for one person might or might not work for you.
I'm a righty, but have manipulated it a bit with my left hand. You'll have to hit the mag release and decocking lever with your index finger. To lock the slide open, it's probably best to put the meat of your right hand over the rear of the slide, draw it back, and then use your right thumb to push up the slide stop. The slide stop on the Sig is the rearmost lever.
To release the slide during an emergency reload, you'll probably want to just pull the slide back, rather than using the slide stop.
M1911