Pixel Dungeon

Specifically addressing your questions on upgrades, since that's what you asked about; here are lots of tips and tricks, but it sounds like you've found a guide that should have many of those. Sorry if you know some of these tips - just laying a few things out there.

There are 15 scrolls of upgrade in the game, three per area. IMO, scale armor can be fine for a win, particularly if you find it already upgraded. As a quick check to see if unidentified equipment is upgraded, I like to throw it on explosive traps - if it's upgraded, it won't be destroyed; if it is destroyed, you haven't lost much.

While I prefer to save most of my SoU for my end gear, it's not totally necessary. If you're using warrior, you can put an upgrade immediately on armor with the seal on it - you'll keep that upgrade through the game, which can be a great help in the early game. Ditto for mage staff - give it at least upgrade early, but it's totally viable to put more to it if you can't find a good weapon early.

If you're feeling frustrated, there's no shame in taking a break for a while - many players (myself included) take >100 runs before their first win.

Random tip: Use Alchemy to create 15 uses of Recycle then recycle your bad potions into Potions of Healing. Sometimes you get lucky and get like 6 potions of healing doing this. Other times you only get 1 or 2.

If you find another Scroll of Transmutation, do it again. I once ended a run with 26 potions of healing.

Other than that, the goal of the game is to learn how to beat it. It's meant to be very hard. I've only won 26 out of 136 runs, though a lot of those deaths were from trying to beat the game with 3 or more challenges enabled. However hard you think the game is, people beat it with even 6 challenges enabled, and many of those challenges are insane. But there are a million tricks to learn for a million situations.

Another random tip: Never step onto a fountain of healing. Instead, drink whatever is in your Waterskin then throw the Waterskin on the fountain. It completely fills it! Now you have instantly have enough dew drops to bless an Ankh.

Go gladiator and upgrade ghost armor to +15 GG (or any random scale/plate)

I just put all upgrades on my staff. Rely on finding a bunch of good wands, long range melee weapon and artifacts. Doing a lot of alchemy to get scrolls of divination, scroll of metamorphosis and potion of mastery. Divination only to not waste any of the latter. I use blacksmith on the highest tier armor I can find and star blandfruits to reach the last level.

That light wand is nice for the last area and dark levels. I always try to stand in doors when I fight the eye enemies and the charm enemy can still be hit by wands.

I never made it to the surface, but beating the last boss works.

I've been playing for years and only won once by using a corrupting weapon combined with a massively upgraded ring of arcana so that just about everything I attacked turned into a corrupted ally and fought for me.

I also heavily encourage stamina potions, elixirs of dragons breath and toxic essence, and challenge scrolls. Make sure to kill all demon spawners on previous floors. If you have good offensive wands, make stones of flock and shock. Throw flock (trap enemy if possible), throw shock at them to fully recharge your wands