I'm still pretty new with all of this stuff, so take everything I say with a grain of salt, but it seems like with all of the fish you plan on having in the 15 gallon tank it would be overstocked.
Also, as far as I have seen and heard about bettas, once they live on their own in a tank for awhile they will become aggressive towards most any fish, so I would personally suggest introducing the betta as one of the later fish into the tank.
You will definitely want to make sure the tank is cycled, I made the mistake of buying a bunch of fish and a tank not knowing anything about cycling, but there are great guides on cycling here,
That shows you the different ways of cycling, it seems like the shrimp method tends to get preferred as easiest, but supposedly the ammonia method is supposed to be one of the most accurate ways of doing it.
From what it seems, it sounds like you've got all tropical freshwater fish there, which should be good as far as water and temperature, but they all do best at temperatures above 74(I believe) so you would probably want to get a heater suitable for the tank.
As far as filtration and plant life goes, from what it seems, enough living plants will be fed by the ammonia your fish will give off, which is taken care of by the bacteria that are grown on the biological filters, even with the plants, you should still have a filter though, and no matter what you should be monitoring the water quality throughout the cycling process. Basically if you go through the cycling information, it'll break down into you needing an ammonia source to develop the first bacteria, which will bring the ammonia level to 0, and create nitrites, the nitrites will feed the second bacteria, bringing the nitrites to zero, and will in turn release nitrates. The nitrates are the main reason for the water changes(which should only be partial water changes) and the nitrates are much less harmful to the water and fish than the ammonia or nitrites.
So to sum up everything I can say(which of course should be double checked by someone who knows)
Make sure you don't overstock the tank! (seems like 1 inch of fish per gallon is the rule, and this measurement should be the adult size of the fish)
Make sure the water can be at proper temperatures for the fish!(Betta can survive in room temperature water, but will do best in a heated tank, and is especially advised for your other species)
Make sure to properly cycle the tank before you stock it!
Adding fish seems like its been suggested as 2 fish once the cycle is done, and like 1-3 every week or so after that until you are stocked to what you want(but not overstocked of course)
As far as the plants I can't offer any advice for lighting or a carbon filter, but I'm sure there's already a few pages in her: http://www.tropicalfishkeeping.com/f...nt-topics-257/
that can offer you plenty of advice on both a new tank, and the plant life.
And from a fellow newcomer, welcome to the forums, and hopefully everyone is as helpful for you as they were with me!