Thanks for a good overview, especially L19-L22, as I never finished the game yet. Now giving it another try after a year away, currently a L13 warrior. The game has gotten much more enjoyable, with more quests, items, and an easier level curve.
Earlier, I played it a lot though, especially on Ironman difficulty, since that somehow was more fun for me in the early game. On that difficulty, I did similar to what you suggest, and ran many of the early dungeons (those I liked) a few times over, for useful loot, XP, gold, and fun. It feels so much better to find a nice item (e.g. Orcslicer, or that rumour cap), than to farm gold and buy the standard stuff. The thieves cave near Kingsbridge was my most frequent destination L4-L8, Maze of Lamth L8-L10. I rarely made it higher than L11, was getting too impatient against high level traps and stun attacks.
On easier difficulty, I have more fun mostly just running the quests, because I can take the more risky ones, rewarding better gear and more XP early on. I did not feel any need to farm until L9, then just occasionally in Mercian Royal Crypt, when I feel more confident rounding off another level there before the next quest. With Hirge, holy weapons, and death resistance items that is easy enough.
I want to finish the game as reliably as possible this time, to get a personal overview, so I play a simple 2H warrior on casual difficulty. Already looking forward to try alternative classes, higher difficulty again, and some personal challenges like the shortest time to collect the shards.