I'm somehow unable to get the full clear (max score of 365). I got the other 3 stamps already, but I always seem to miscalculate somehow. My strategy is to get 0 hearts and then either level up or get a full health boost and repeat. Do I need to do something else as well? Certain monsters at specfic health levels or something?
It's important to get at least some of the free exp drops early so that you can save your health scrolls as long as possible. HP = EXP, but things like chests and the egg give you an advantage in that calculation. Always try to drain your HP to 0 hearts before leveling up, and if you have the choice between leveling up and using a health scroll, level up. The more health you have, the more health a scroll is "worth", so saving them as long as possible gives you more total effective health. Also, you want to kill the lich as SOON as you have 10 hearts, or as close to then as possible. That gives you a massive load of experience you can use to carry you through the next few levels without using scrolls.
Very good - that is of course true!
In practice there is very little reason to not blow up the mines immediately when it becomes possible. This is because one has to do it before having to resort to the next health scroll (the XP from the mines is better), and at that point of the game, since one has >= 10 HP, then there are no things on the board that can kill the player at health. (only mimic chest, but it makes itself known on click) So ambiguities are not that important anymore.
It's not a 100% guaranteed possibility like with earlier easier versions. Never heal up unless you've depleted your health pool. Minotaurs always guard a chest. And chests are always guarded by minotaurs. Guardians are 1 per qudrant. Use that info when calculating exploration risk, but don't forget the 9HP and 11HP oddities. Level up instead of healing whenever you can. THE VERY MOMENT you hit 10HP, take out the bomb lich and score another easy level up. Look for the 8x8x8 pattern of the slime wizard and deep strike on his butt (You can blind jump into a square). Learn the ? gazers patterns and they can similarly be nuked from orbit with pinpoint precision. Try not to waste HP on walls until the very last sweep and remember you can kill the dragon for 13G without ending the run which comes in handy on that very last cleanup pass. Play cleverly and take every advantage of the numbers. I can pull it off maybe 30% of the time.