To answer some of your concerns, Peg:
-- Crossword constructors in general are very generous about sharing their knowledge. However, most discussion takes place on the CRUCIVERB-L mailing list. If you're interested in joining this (free) list, you can find more information by clicking on Navigate > CRUCIVERB-L
in the left-hand panel. But fewer experienced constructors visit this forum, and they are most helpful, especially by critiquing puzzles by new constructors in the Post a Puzzle
-- Many of the people who visit this forum are new constructors, and perhaps aren't in the position of offering much help.
-- Requesting comparisons of different software packages is somewhat futile, because I think most constructors started off with one package years ago when there was little available, and never found any overwhelming reason to change. Plus, nobody is paying anyone to do a detailed, feature-by-feature comparison.
-- If you decide to use a software package that doesn't create one of the commonly acceptable formats, not to worry. You can manually convert any puzzle to AcrossLite without a lot of effort. Or, easier yet, just print it out and submit by snail mail.
-- Usually, experienced constructors don't use autofill to do the complete job; they might use autofill to verify that a grid is actually fillable, but then switch to manual fill to select the most interesting words for fill.
-- Whether or not to get all the bells and whistles I think might depend on how deeply you want to get involved in construction. Perhaps you might want to start with a vanilla version, then upgrade to a full version if you decide that you enjoy constructing, find it satisfying, and would like to continue.