I've seen lots of posts/responses over the years about how to paint a ****. Be it a bike, a car, a family room, whatever. It really comes down to three things; preparation, tools/materials and skill. I've seen people asking about how to get "professional results". If it is your first time painting *anything*, it is unlikely that you will achieve professional results even with the best tools and materials. Be realistic on your expectations relative to your experience.
For a bike, remove as many obstacles as you are mechanically comfortable with; wheels, brakes,handlebars, seat, chain, crank - as much as you can do. If you can even get down to removing the bearing races, that's even better. Take a lot of time preparing the surface. Get rid of any blemishes at a minimum, such as rust, chips- things that will show through a new paint job. Mask off anything you don't want to paint. I believe in priming before painting. There are always areas where you sand down through all of the paint and even where you don't, priming the whole works will make for a more uniform finish. Before you prime, follow the preparation instructions to remove any residue, such as dust, oil and grease. I like to use automotive grade primer that I can wet sand to make sure that I have a good, smooth base. For the paint I am now using, this requires a rub-down with mineral spirits before priming. Wherever I miss a blemish, I can re-sand and re-prime. Once I'm happy with the base coat, I top coat with the final finish. I wait a while (many days or a few weeks) before I try to reassemble the bike. The longer you let the finish cure, the less likely you are to damage it. I've done this for a few old, sort of classic bikes with positive results using Rustoleum or similar spray paint. If I am ever lucky enough to have something really special, I would leave the task to a professional.
So, if you are already comfortable with the disassembly and assembly of a bike, painting is not really that hard. I am now painting a 1965 Sears Spaceliner and am about to reassemble. It's taken me a few weeks of time in between a lot of other projects, but I'm not really focused on it and I'm in no hurry. I'm doing the same for an early 50's Western Flier for my wife - it needs a little more patience.
At the end of the day, unless you have something that should really be preserved in its original state, it's just metal and paint - you can always start over. Good luck!