Something you should look into carefully is local laws and ordinances regarding DIY painting. In many (most? all?) urban California areas, it's virtually impossible to set up and spray a car in your own garage. If caught doing it, you might end up paying more in fines than it would cost to have the job done professionally by a shop. In fact, some types of paints and spray equipment are banned and illegal here, vendors and manufacturers won't even ship them to a California address.
I see you are in Oregon, which is probably a bit less regulated than Calif. But, I'd still suggest checking into this thoroughly and carefully.
Quality of work in shops can vary hugely, and price along with it. If at all possible, look at finished examples of their work and decide based on that and their quotes. A good shop will also work closely with you on what you can do to prep the car as much as possible, to help keep the price reasonable. The other side of that equation, some shops might insist on doing much of the prep work themselves, so they don't get unfairly blamed for any problems later on, after the final paint is on.
There are a number of good paints out there. Look for major name brands and research them on the Internet. Different shops use different lines of paint, and might recommend one brand for a metallic, another for a solid color, for example.
When looking at quotes from a pro shop and comparing it with DIY, be sure to consider the "real" cost of DIY. First is that there's a lot more equipment involved than just a compressor and spray gun. The air supply needs to be dehumidified and oil free. The painting needs to be done in a completely dust free environment. You need to protect yourself from fumes and paint during the application. Most states and cities have some sort of requirement to control and filter exahust air. The finished paint sometimes needs to be heat cured. Etc. And, there is a pretty steep learning curve involved... Painting is a real art that takes practice. Mistakes cost a lot to correct, or devalue the car if left uncorrected.
You might also check out local community colleges, to see if any have auto painting courses. They might have facilities to help keep your investment down, and some expert guidance would be very helpful for anyone doing a paint job for the first time, or even for someone coming back to painting after not having done it for many years. (BTW, the same community or vocational college might have courses on body repair and welding, which also can be very beneficial.)
Finally, some folks turn their cars over to community/vocational colleges for body work and painting, by the students under the hopefully watchful eye of the instructor. A bit risky I suppose - a little more-so than going to a hair styling school for a trim, but probably less risky than going to a dentistry school for a bit of drilling. It might be a way to get a good paint job at a bargain price!
Best advice I could give on color choice would be to stick with an original Triumph color appropriate for your year and model, if not the exact orignal color that was used on the car (if it's a desirable color... some might not have ever been all that desirable, or might be "out of fashion" today). An original color, assuming it's a popular one, will generally give the best value if and when you ever try to sell the car. "Resale/arrestme red" is often chosen for sports cars, although it seems to me to be a bit overdone, looking around at most car shows. OTOH, bright red does look great with popular tan interiors.
Color choice is ultimately yours, and your preferences will guide your final decision. You might decide differently if planning to sell the car quickly, or to keep it for many years.
You can get at least some idea of colors specific to your car online at
www.paintscratch.com, but keep in mind that even with a color-calibrated computer monitor these are likely of limited value. Any color you choose you may want to have a small panel sprayed, and then inspect it indoors and out in the sun, after it's cured. There is some variance in any given color formula from brand to brand and from mixer to mixer. Even the method of curing and the color of primer used can make a big difference in the final appearance of many topcoats.
In terms of prep, a common mistake is overdoing high-build primer sanding to the point that sharp body lines are dulled and concave shapes are over-filled. Watch shows like "American Hotrod" and "Overhaulin'" and see how they spread a thin coat of Bondo over the entire car, then block sand it to form uniformly crisp edges and even out any ripples in panels. A guide coat of paint, with further block sanding afterward, is often used to help visually identify any problems, too.
Disassembly is better than masking, if practical. And, when spraying the exterior topcoat on a car that's partially disassembled, I always liked to position all the loose panels in their final orientation. In other words, the hood lying flat, fenders and doors upright. And, I positioned all the loose panels around the car so that they got painted in the correct order, too.
Finally, something I've often heard at car shows... "Classic" cars might look slightly odd with too glossy a paint finish, such as some modern clear coats. But, this is again pretty much a matter of personal preference.
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