I would wait for the hardcore mode before you try playing such a limited run. I agree many things are pretty unbalanced, but limiting your options will just make the game more tedious and boring. Larian should be aware of the imbalances like elemental shields and some of the talents, so hopefully those will be rebalanced. I guess I mostly think you choice to play without legendary or even magical items at all would really reduce the satisfaction of many encounters, since loot is one of the biggest draws to playing RPGs (at least for me). But I suppose that would make the game a lot harder, since you'd be losing out on a whole lot of stats and resists.
You're limitations on skills and talents would also limit your options. Limiting skills trees to 4 might be okay, and maybe limiting a character to two skill trees would make choosing skills more significant, but not letting characters overlap skills might be a bit extreme. There are plenty of garbage or non-game breaking talents you can give your characters.
I think the codexes are okay, but should just be muuuch more rare. I found 10 of them or so, most of them in barrels and boxes. A pure mage has basically no use for perception (especially since leadership basically guarantees your initiative), and 4 more points of int is quite a boost. You should find maybe 2 codexes, max. Or if they're for sale, they should be absurdly expensive (although the whole economy needs to be reworked for that to have any effect.)
You can eliminate savescumming without adopting a tedious and arbitrary system. Just don't save in combat or before RPS rolls or before chests or anything like that. You should accept non-ideal outcomes, but I don't see the point in making yourself replay whole battles or areas just because there wasn't a questlog update.
