I woudn't bother with most of your ideas, but maybe that's just me (sometimes less is more....). I wouldn't take psychedelics, or recomend anyone I know to take them, on a comedown... but maybe i'm just strange. Smoking weed until you snooze I guess works pretty well though, actually. 5-htp I would only take at least a good few hours before sleeping, and tbh i'd wait until the next day, I find it can make falling asleep hard. Generally I don't find MDMA that hard to sleep after, though, I quite often stay up pretty late partying and doing stuff (late night wanders and things), so sleep comes naturally, as I mostly take MDMA or clean pills.
GHB does work really quite well (and of course feels GREAT mixed with MD), but then I use GBL, and that has a definite effect on your body, like making you have a dry mouth and a sore stomach the next day sometimes. Benzos work kinda well too, although I don't use them often, but I reckon valium/xanax would work great for me most times... then again, diazepam can make ya feel a bit groggy afterwards. Alcohol too.... but hangovers on top of comedowns suck, so I usually just hit the bottle the next day if I feel that crap, and don't have much to do. Ketamine works well actually, I find, although I don't like doing more than bumps nowadays, but it chills and mellows things out, which is always good for sleep.