You'd need a locomotive boiler to produce enough steam to run the apu, even if it runs at all as white hot dry gas requires somewhat different fluid dynamics than warm wet steam. You don't get anywhere near the volume or pressure of steam from a "primitive boiler". Anyway, why do all that when you have 1000gal fuel?
Diesel generators are seldom carried on passenger flights I fear. They are far too heavy- you buy them where you need them.
You deployed the RAT. It will have been destroyed in the ditching.
Aircraft generators are far, far too big, heavy specialised and and complex to run off a heath robinson windmill I think, the RAT gen might just work (if it miraculously survived) but you're going to need a machine shop to modify the gearing/drives and build the windmill which would have to be pretty big to produce the power to drive even the rat gen. Did you have a machine shop in the hold too? Also on a modern aircraft like a 777 gennys are controlled by black boxes elsewhere. They produce 400v ac. Did the inverters miraculously survive the salt-soaking too?
No tools on a 777 unless in baggage. Few aircraft mechanics would carry a hacksaw in the sort of "light" toolkit they'd use on a short fix-it trip. Its just not a tool used in aircraft maintenance.
On a busy 777 someone is going to have a satfone in their pocket
I fear you'll have stretched credibility far enough (and then some) just by ditching at sea and managing to slide it up the beach. All the rest is making it become comedic.
If you have to do the Flight of the Phoenix stuff leave out the seawater at the start is my advice, and even then tread very very gently, a digitally controlled 777 isn't a tin and rivets Boxcar!