Question 1) While downloading you are automatically seeding (called being a "peer").. after the download finishes you should force start the download again, which will initiate seeding. (so when people download from the link they are downloading from you and 5-10 other people.)
Question 2) Any DVD burning software should do. Nero Ultra is what I use, but ther are probably free options on Download.com (or others like Windows Media Player pre-installed)
Question 3) There are ways to create a .mp4 file to use with media players... the problem with DVD ready files is that they are generally split into several different files. The easiest method (to get a clean, individual file) is to compile the files into an .iso or .bin/.que file and convert it to a .mp4...
and talk more.. 