No worries bout the hundred questions! It just means you're getting a novel back in replies haha.
Okay for cycling your tank, basically what's happening with that is that you are growing a colony of Beneficial Bacteria, or BB. It takes about a month to grow them and there are several ways you can do it. There are two popular ways though, one is having the fish in the tank, and another is without fish.
You can put your Betta in there but you need some sort of test kit with ammonia/nitrite/nitrates. You need to keep the ammonia down and never let it go over .25ppm. Once you see it hit .25ppm, you need to do a small water change, this might happen every few days so this is why it's prefered to do a Fishless Cycle if you can, but don't worry about it if you can't. There are plenty of us on here that use Fish to cycle our aquariums :)
Visit this link again, read the first posts and then comment #4 to get an idea about cycling. You're more than welcome to read the others if you like as well :D http://www.bettafish.com/showthread.php?t=111960
But after your tank is cycled, on water change a week will be perfectly fine for him, about 25% of the water. You need to use a siphon so you can get through the gravel to clean it thoroughly.
And yes you can keep him in while changing water, many Betta's will flare at the siphon or try to bite it (my girls do lol) but they'll be fine. However if you're doing a 100% change, then yes, you need to take him out :)
You can have as many plants as you want! The more live plants the better! You can also get any plants you like. Some of the more easy ones that don't need much fertilizer are Java Ferns, Anubias, Hornwort, Anacharis, some Crytocornes and wendtii (although most red plants need very high lighting, but they'll just be green if you don't have high lighting), water wisteria is a great one and Water Sprite.
Just be careful that when plants start to rot, just clip off those leaves either with scissors or with your finger nail so they don't pollute the water :) Some plants will "melt" when you put them in, but don't worry it's just getting used to the water and will grow back leaves soon.
There are two types of baffles that I like to use, here is my favorite: The water bottle Baffle: http://www.bettafish.com/showthread.php?t=30139
And then the sponge baffle: http://www.bettafish.com/showthread.php?t=56100
Oh also, the more live plants you have, the easier it is to keep the ammonia and nitrite levels down because plants feed off of those things. Well specifically nitrates, but ammonia is converted to nitrites with the help of the BB and then nitrites are converted to nitrates which can be taken out with water changes and plants eat them. So if you've got lots of plants, you won't have to worry too much about cycling :D