The headstock normally has a larger taper to provide a larger through bore in the headstock, the tailstock is smaller because it's principle purpose is to both center and provide support for longer pieces and to allow attachment of a drill chuck, taper drills, reamers, tap and die holders, other tooling etc. to work on the end of pieces. The larger the lathe the larger the tapers will be.
Other things being equal, bigger is better.
Collets are, IMO, sort of optional for most lathe work with 3 or 4 jaw chucks being more useful for a larger range of holding (YMMV). I've used a small lathe for all kinds of various work for years and don't have a collet chuck system, one of those things that would be nice to have but not justifiable cost wise for what I do with what I already have. A collet is more precision than a jaw chuck if you are intending very high precision work. A Jacobs (drill) chuck is usually mounted on a taper for use in the tailstock to hold drill bits, taps, dies, reamers, countersinks, etc. and a reasonably good one is more than adequate for anything intended in a home shop where ultra high precision is required (ultra high precision being above the skill level of most non professional machinists and hobby lathes anyway).
This may be of some help in answering some questions about
Lathes.