I'll share some details of my work in fitting a windscreen/fairing to 'ol Bengt Phorqs R90 and perhaps address a few of your concerns.
I encourage everyone that plans to paint a fairing, tank, fenders, car, whatever... do not buy your products from a big box store. Trade with a legit body shop supplier and explain what you want to do. Listen to them. They know their business.
An example is that crap glazing putty sold alongside LED license plate frames. There is a difference. The cheap stuff is notorious for bond failure
after priming and paint. Also, there are specific primers for flex objects -like your fairing- and flex additives for paint. Pay a little more and do the job only once.
After removing the paint from your Wudo and exposing the gelcoat, yes, sand it. I used a 320 grit
wet with a soft sanding block. Try not to sand without a block of some sort as fingers can actually cut grooves in the substrate if aggressively over-worked. Just clean the gelcoat in prep for multiple coats of sandable primer. Avoid sanding through the gel coat and exposing raw f'glas fabric. That'll create more work.
Should there be any deep scratches, fill with glazing putty and re-sand prior to prime.
Follow the required reduction of the primer and paint. Reducers are available for various ambient temperatures. Again, the body shop supplier will be able to steer you to the correct reducer for your project.
Mike's fairing and screen have been matched. The lower is ready for gel coat sanding.

Most primers are to be sanded dry. Prepare for the mess and wear a respirator. When your paper clogs up, throw it away and get a fresh sheet. You're wasting time and reducing the quality of finish by being overly frugal with sandpaper.
I shot three coats of primer, sanding each one with 320 grit
dry. Pick up a package of tack cloth rags while you're buying paint supplies. Blow off the dust, then
lightly run the tack cloth over the fairing.
There are dark and light colored primers. Pick one based on your fairing color choice. Also, light colors permit easier viewing of tiny pits that may have escaped the glazing putty.

Ninety percent of the work in a great paint job is done
before shooting color. I find the color work to be sorta anti-climatic after investing the time and energy in all the prep work. But is is way cool seeing the results. Plus, Mike bought the beer.

Bottom line... There's no black magic involved. Just avoid rattle can jobs on a fairing project. A proper compressor, gun and cleanliness will pay huge dividends in quality work you'll be proud to say, "
I did it".
I have painted cars, motorcycles and two aircraft. You have to start somewhere and your fairing sounds like the perfect job. Really small stuff and, sometimes, big stuff can be challenging to the novice. Go for it. Last thought... Don't worry about a small sag or a bug landing on wet paint. Color sanding -that's wet sanding the paint- cures many flaws.