kings - yes I expect 'stay' will work in exactly the same way that I use 'wait' and as you have already started with that, it should be easier.
I just use 'go on' as the release command - I didn't give much thought to that one, it just evolved as I said it naturally.
At our first training session the trainer did advise drawing up a 'doggy dictionary' so that the whole family knew which words meant what, and so that you could easily check for inconsistencies. It sounded daft at the time, but now I am thinking it might be a good idea!
spam - I had a similarly frustrating day of attempted gardening a couple of weeks ago, which prompted me to buy a doggy play pen. I know this makes me sound like a crazy person, but it has been so handy - 8 big panels, one of which has a door in it, by Savic for about £40. It has been so useful - I pop her in it in the garden so I can get on with things, or in the house if the doorbell goes or the children want to play whilst keeping all of their limbs intact.
We are walking her with a collar and lead, and I share your frustration - we are also doing the stop/start method, and have seen some improvements but it is still impossible to do a 'quick walk'.
slinkyboo - not sure, we had the same problem, we weren't very far from home but got stuck in horrendous traffic and ended up being on the motorway for about 3hrs. She hadn't had all of her vaccinations yet, so I kept getting out of the car and standing her on a towel whilst giving the wee command. Absolute madness, and it didn't work - she was bursting by the time we got home. The only thing I would say is that they can only hold on so long before they simply have to go, even if they are not comfortable with the location, so surely no physical harm? Surely?