Dennis,
Only experience will help you pre-determine how much paint to mix, and I still wind up with more than I need just to be on the safe side. Here's a secret trick... You can store mixed 2K paint in the refrigerator for several days before it starts to thicken. I wouldn't recommend leaving it for more than 2 days for spraying, but when I painted my cab I brushed the areas I had taped over (center WS post, inside of cowl vent, around rear window opening) about 5 days later and it worked fine.
However, I have poured out a lot of mixed paint when I knew it would be a long time before I'd be painting again, Yea, it sucks to pour money down the drain (in a manner of speaking) but it sucks worse not to have enough to finish.
I was really sweating painting the roof of my cab. I thought of ways to paint it in sections but there is no seam anywhere that isolates one panel from another. So what I did was every time I put a coat of primer on I practiced how I would get even coverage on the roof. I used a ladder and it worked out, in fact the paint is smoother on the roof than it is a couple other places. My only advice is use a ladder and turn it in such a way where your arm that's holding the gun is closest to the cab. I'm a righty so that meant I was facing the rear of the cab when painting the passenger side and facing the front when painting the driver side. Holding the gun square to the surface is critical so practice, even if it means with an empty gun just to get the experience.
The pot life of paint depends on temperature and that information should be available on the data sheet. Regardless, you should have plenty time before it starts to thicken... it dries a LOT faster on the part than it does in the gun.
I've never used a cup liner.
Clean up is a PITA, no matter how you do it but get used to it because it's the nature of the beast.
I pour out what's left in the cup and put about an inch of lacquer thinner in, put the cap on, shake (hold your finger over the vent hole) and then just spray until it's empty.
Then I put another inch or two of lacquer thinner in the cup and use a 1-inch bristle brush to clean inside the cup and cap. Then spray until it's empty.
Next I put another inch in the cup and use shop rags to wipe down everything using the thinner in the cup. Then I spray out what's left until the cup is empty.
Next I unscrew the cup and nozzle and clean the nozzle parts with a bristle brush and blow it clean. Look into those tiny holes and be sure they are clear. I also remove the screen filter and clean it the same way. Then I use a bristle brush to clean the gun where the cup screws on.
I never cleaned the needle until recently and was happy to see no appreciable build up, just a ghost of color that wiped right off. Just to be on the safe side, I say clean the needle each time too.
When I'm done will all that I assemble the gun, put about a half-inch of lacquer thinner in the cup and spray until it's empty. Use a clean rag and thinner to wipe down the entire gun but be careful because lacquer thinner will frost the plastic lens on your regulator.
I know it sounds like a lot of work... because it is, but that gun has to be perfectly clean to work properly.
Just remember that once you are done no one is going give a fig over how much work you had to do to get to the finished job, they are only going to judge you by the finished product so keep that in mind at all times and discipline yourself that "good enough" is NEVER good enough. Don't cut corners, do the absolute best you can. That's the only way to minimize the amount of "mistakes" you will inevitably make.
