With real-life events being cancelled, I have more time to play games, and I think I need something that would last a long time.

I am planning on using OpenMW instead of classic Morrowind, but with some tweaks to the source code to fix some of the uglier aspects of the game:
* Level ups will give +5 to two stats (instead of bonuses to 3 depending on your actions during the previous level); reducing the number of stat increases to 2 to simulate a non-optimal build that should at least keep up with NPCs while removing the uglier part of stat growth and the missable stats issue.
* HP gains from Endurance will be retroactive (though I might still have them just be based off the base value). Perhaps have HP be equal to (Strength + Endurance) / 2 + Endurance * Level * .1, unless you'd suggest a different formula. (Note that I might delay increasing Endurance with this change, unless I really do need HP sooner.)
* Effective alchemy (that is, Alchemy + Int/10 + Luck/10) capped at 120, which is the highest value obtainable in vanilla without any fortify effects. (Fortify effects will still work up to that point.)

So, how do these tweaks sound? Any balance issues I should know about?

I'm not 100% sure, what I'll play, but I do want Enchant, and possibly Restoration, Conjuration, and maybe Axe as major skills. (Axe is good for the Bound Axe spell, which is easy to get and quite useful.) I've usually played a female Orc, but maybe a female Breton with the option that removes racial effects on movement speed? Also, there's the question of choosing a birthsign; maybe Lady or Atronach, or perhaps Mage or (if playing a Breton) maybe even Apprentice?

It's a long time ago, but I distinctly remember sitting with three friends and spending the whole evening just exchanging hilarious exploits in Morrowind... Not sure the list was finite really. Ofc Alchemy was the most outstanding offender - in more than one way.
Has the infinite physical attribute growth during that infection been patched? How about refreshing all Your mana by temporarily lowering INT to 0 (0/0 = 100%)? That's Destruction ofc, but nice as a secondary effect for pretty much every spell. Wasn't there a glitch allowing You to keep summoned weapons? It really has been a long time. Did they really patch so much?

As far as I am concerned the whole fun in the "game" was to find the myriad of exploits and have a good laugh! That's actually what I genuinely loved Morrowind for. That game was an open world - wide open like no other. You could say even the simple fact any run-off-the-mill mage could open every lock in the whole world was a rather huge balance issue. I mean: What are the thieves to say?
In a way it is sad Bethesda became less daring and more conservative in their uptake on an open world in later titles. A joke of a game is way better than a bad game I say!
Once they were daring pioneers... Oh well.

OpenMW is an open source third party rewrite of the original Morrowind engine, and therefore has some different characteristics with respect to certain bugs and edge cases. So far, what I've encountered is:
* No 0 duration enchantments; if you leave the duration of a "Cast on Use" enchantment at the default value, you get a 1 second duration.
* Merchants with restocking leveled lists don't seem to restock them. (I think I'll make a little mod to give the clothier in Balmora restocking Expensive Rings because of this, so that I have a supply of lightweight items for cast on use enchantments.)
* The Lady birthsign does not actually give you more HP when leveling up, making it basically useless. (Apparently, you can at least get your Endurance and Personality up to 125 with this birthsign, but that doesn't make up for the lack of HP from it. Also, there's apparently a mod to revert this behavior.)

I've read about some other changes, like making blindness reduce accuracy (instead of increasing it) and tired characters having a lower chance to repair items (as opposed to a higher one).

Yes, there is the trade-off between freedom and balance, and Morrowind and Oblivion took very different approaches. For example, Oblivion's developers overreacted to the super potion exploit, making the Fortify Alchemy effect useless; my proposed change (which I haven't implemented, unlike the other two) would allow that effect to work, but not beyond the maximum potion effectiveness you'd get without it.

Also, don't forget that Morrowind has that one scroll you get early on that temporarily raises one of your skills 1,000 points (in a game where the normal skill cap is 100); you would not see something like that in Oblivion or Skyrim.

Edit: Also, did you seem my other topic on this forum where I compare the super potion exploit to a similar (but not game-breaking) trick in the game Dungeon Master?

Actually I haven't, no. Which thread would that be?

https://www.gog.com/forum/elder_scrolls_series/one_similarity_between_dungeon_master_and_morrowind

(It's still on the front page.)