Just go for it... Don't be too discouraged with your first attempts. Just keep the covering pattern simple.

I can't comment on using sanding sealer, but my first inclination would be not to. I've had good covering success without it. I've tried to put covering over painted wood, and have had mixed results. Sometimes the iron melts the paint.

The best preperation that you can do for yourself after sanding is to thoroughly vacuum the sanding dust off from everything, then go over it with a tack rag for good measure. You can't cover dust. You'll be surprised how even the smallest imperfections will show through.

When you iron the covering down, 'burnish' it with a soft cloth to work the adhesive into the wood. Keep the cloth soft... the covering will scratch, though most people won't notice it - except you.

I'm not sure how far into modeling you've come, so pardon me if I'm repeating what you already know. Use a light colored pattern on the top of the wing, and something darker on the bottom. I usually put a spanwise pattern on one side of the wing, and a chordwise pattern on the other side. It doesn't mnatter which pattern goes where. I've also had good success with a checkerboard pattern on the wing bottom, but the checks should be about 3" or larger to be seen from the air.

I've got a woodpecker and have used it, but have to admit it doesn't do that much. If you've got one, use it. But I wouldn't go out and buy one. You might come across one at a R/C flea market for a buck or two.

Everyone develops their own techniques. I use the trim iron and heat gun - only use the large iron for large surfaces. Other guys won't touch the gun or the trim iron... you'll develop your own technique. Use what works best for you.

I'm sure that a lot of other guys will drop by and give you good advice here too.... and some not-so-good advice. Just remember, everyone's an expert here, including me :-D

Definition of an expert - someone who's been doing it for 15 minutes longer than you have....

Hope this helps.

Bob