There's been some good advice listed above and I wasn't going to reply to this thread when I saw the title of how quick can you do a shell as I'm one of the slowest on here although I did knock 4 out in 12 hours once... nearly killed me mind you LOL.
Anyway, it's not always the dark art that everyone makes out. Yes it is "ideal" to have a nice ambient spraying temperature but I work in my garage, no heater, if it's cold I have a coat on but the air in the garage is cold. So to combat this I warm the shell with a heat gun ( a hair dryer will do ) before the first coat, then I dust a coat on and dry that with the heat gun keeping the shell warm. Not had any problems with that.
Liquid Mask is the nuts but if you force dry it I personally find it doesn't come off so well, also it takes time to get it on and dry it out so for quickness I would use either masking film or masking tape pushed down real real well and very firmly. You can get nice clean lines with it. If you can get the wide Tamiya tape that cuts lovely but it is expensive
I dare say it's not good to breathe in anything but fresh air, however these paints are only water based and you're spraying so little with an airbrush a mask isn't vital, if you've got one use it, if not I wouldn't worry too much unless you plan on doing this day in day out. I've been airbrushing all manner of stuff for years, I'm too old to remember, probably about 24 years now, only ever worn a mask when I got the spray gun out, never worried about it, not had any problems for it *keels over and manages to hit send with his dying breath*
Try and work Dark to light, however if you have pinlines or fine masking I would do that first. If you have to put a dark colour behind it back the lighter colour with white and then grey or silver to cover it.
Get a can of ligher fluid, the normal one, not the aerosol, use if for removing any masking residue from the tape and any grease finger prints.
Nitro Block is good for nitro cars but to be honest you can get away with a white aerosol, make sure you leave it to dry out well before hand, over night at least or kane it with the heat gun and some white Plastikote from a spray can, again, light coats, dry inbetween. You probably want to wear a mask for that or do it in the garden and make sure the wind is blowing away from you.
Good luck
