If you plan a Diy , its simple ,Only if you are Handy ,Can do it over the weekend , or call friends for help and later treat them with a Bear ! lol

You need 1) a paint brush 2) a ladder. 3) paint

There is nothing special other than painting in the direction of the grain of any texture.

I personally wouldnt use satin because I think its too shiney. Semi gloss is traditional for trim but depending on the home and look flat is fine too. Oil based are more durable but have drawbacks that IMO make them unneccessary for most homes and the gloss they can have looks a bit low rent to me sometimes. Just make sure when you are at the store to specify EXTERIOR flat or semi.

Really most of the work is climbing up and down the ladder. If your house is a two story and the trim is up very high, maybe anything above 20 ft, call a professional who will have ladders better suited for it.

Its really a job you can do on saturday

White siding, as in wood, or vinyl? If it's wood, Larry's right. If you have loose or peeling paint you might want to scrub that off with a wire brush. Otherwise it's just the right paint.

If your trim is vinyl you will want to talk to a pro.

Sorry. I should have specified. Our siding is vinyl. That's why I was so confused on how to paint it.

Your confusion is totally understandable and a whole 'nother can of worms. I would look into a professional to help you. If that's an out of budget idea, talk to an experienced paint clerk and most of them can give you some recommendations, at least.