I wouldn't worry about selling modules too much - often it's difficult to work out exactly what modules are right for you until you actually try them with your other modules...
as for multi-track recording probably the easiest way is to use a es3/8/9 or bored brain optx depending on the audio interface that you already have - as these are designed to work with modular levels, although quite a lot of regular audio interfaces will work perfectly well with just attenuated (possibly in the audio interface itself) signals
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities