We have a 30 gallon sprayer with 12 volt pump that we use strictly for paint. We have a nice handtruck for moving large b&b trees, it moves the tank around sites bretty good when you cant get the truck close enough (hose is 40'). I definitely would recomend not using turf paint in your ragular spay set up, the paint has a tendency to thicken up in your hose, gun, nozzle, when you are done spraying. We try to thoroughly rinse the tank 2x after we spray and thoroughly rinse the lines and gun.
As far as coverage, it varies greatly. If there is pretty thick grass and it's 2.5-3" or so long and you're just trying to darken it up, you can get about 3k-4k out of a gallon. You can spray pretty much anything other than the dirt; thatch buildup, dead grass and pine needles in the lawn will all hold the paint. If the grass is real thin and you are trying to spray, this other materal they will suck up alot of paint, you'll get about 500-1,500 ft a gallon.
I want to say off the top of my head, the label says something like 3-10k per gallon. The only way I can see that is for bentgrass greens.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!