…“and a place to stand”, can we put out the Sun like a barbecue fire or a burning crap-filled brown paper bag?
I really doubt it. 
Nope. That much water would compress and heat up under its own gravity to the point that the hydrogen (from the water) begins to fuse into helium. You’d just end up with a bigger star than you started out with.
Squink has done his homework. However, yojimboguy better reread the chapter on scale.
All you need is water and open space and you can CREATE a sun? In fact, one will create itself with no further action?
Ok, how bout a big enough block of ice, melted at a fast enough rate to supply our hose?
How big can an interstellar iceberg get before its structure collapses under it’s weight. Could you put some kind of heat pump in the center to make a propellent?
The oxygen is optional. All you need is a solar mass or so of hydrogen and it will contract under it’s own gravity to form a nice little star. When the gravitational compression heats the hydrogen to 30,000,000 degrees or so it begins to fuse into helium. The energy thus released counteracts the gravitational contraction, and blows any remaining nebular gases out of the system. Here’s a nice picture of a new star doing just that.
Larger than Jupiter and smaller than our sun would be a rough idea of the size the block of ice should be.
I think it goes without saying, but I’m gonna say it anyway. Combustion and nuclear fusion are very different processes. Water removes one or two elements from the fire triangle (fuel + heat + oxygen), typically heat, but it also can smother a fire. It’s a little harder to stop a nuclear fusion reaction on a stellar scale. (This is what’s known in literary circles as understatement.)
So does this mean that my dream of creating an ocean big enough to see if Saturn would float is just a dream and couldn’t be a reality?
You could probably still do it if you used some antigravity generators to keep the ocean from folding up on itself. Or maybe added enough jello to make it thick and rubbery ?