Thank you sm, that's some great advice. I bought the boat used and haven't been able to find any other hobie 20 sailors around so tuning has been all trial and error. I appreciate it!
In my experience, all of the other controls provide minor "tweaks" whereas the downhaul is the major adjustment on the 20. The comptip along with having some prebend on the mast allows you to get a huge range by simply using the downhaul. Most people run a cascading downhaul system to reduce friction. Upwind, the skipper steers through the puffs and lulls while the crew plays the downhaul constantly, the mainsheet is only eased in major puffs. The traveller should remain centered until the point that the wind is so high that the downhaul is maxed out, the jib cars are travelled out, and you still have to sheet out. Only after that point should you ease the main traveller out, othewise your upwind angle will suffer.
I'm not too sure on the current thinking about mast rake. We ran with the mast raked as far back as the stock forestay would allow, but never added any adjusters to the forestay (although I recall folks doing that). On the 20, pitchpoling isn't generally an issue until the wind gets up to the 20kt range.