For an 020 with 4MB RAM I'd strongly suggest sticking with OS3.1 man. OS3.5/OS3.9 isn't pleasant with an 020 and especially 4MB RAM (unless you strip a lot of things that I don't think it's worth doing).
ClassicWB Full is a really awesome ready to play environment with everything you need. It looks great also and runs just fine on you 020/4MB Amiga.
Or if you prefer more minimal and neat 3.1 looks... you should really try Gulliver's
BetterWB addition to the stock Workbench 3.1.
