Sorry for taking so long to reply! To unlock the stages you just need to collect a specific number of gems. All you need to do is clear your save game from the game menu, then when you pick a character you will see each stage is locked except the first stage. It will say 0/4 or 0/6 or 0/12 or whatever on each stage. That is the number of gems you need to collect on that stage in order to unlock the following one. So you can get all the exact numbers in the game by clearing your data and going to the stage select.
Hmm, OK I'll add all the consoles so that people can tag their runs properly, but otherwise I'll leave the two categories as "PC easy" and "Extended cut story" since that's the main difference in what is being played through. Otherwise some consoles will be slower or faster and it's up to you if you want to run the same run on slower hardware.
Sorry for taking so long to reply. I would say submitting under the PS4 category is fine, unless playing on a PS5 changes something about the gameplay (faster load times, save state features, etc).
I can get in touch with GrassiNole if you need to submit something.
Cool. I was thinking of doing that yesterday but noticed the guides accept just text so I left it. The guide isn't great for speedrunning, but it does show the most direct route, most of the places you can get items, and the more tricky parts.
Health management is a little tricky, since you have to keep checking your inventory to know what's happening, but ultimately fairly simple. The fastest route through the game lets you pick up health/sanity recovery items without going out of your way in many spots. Then you just use those items whenever you're in danger. I think there is only one spot in the game where you're very likely to get hit at least once, there you'll probably use an item or two. Then in the apartment there is also one enemy which you have to literally walk through and they'll most often hit you, but not too hard.
Of course, in the final area you'll also need to heal once and possibly recover sanity. If you watch my run and speedrun tutorial on youtube you can see the spots where I grab recovery items.