...(litany of major problems caused by the mod)...
...for me the game in unplayable until i can make the party i want, because i refuse to build my main characters around their companions to have the party set up I desire
Got to say that this viewpoint is indecipherable to me. The game is "unplayable" for you because you have injected mod code into it which seeks to alter the fundamental structure of the game as it is intended for play by its authors & programmers. Many RPGs allow for the player to set up his party according to the ideas you've espoused here, but it must be noted that many RPGs also do things *differently* from your interpretation of "old school"...and yet they are no less "RPGs" for having done so. IE, there is no set-in-granite, single-rule, cookie-cutter textbook for an RPG adventure to follow, thank goodness.
In this case, the changes the mod is attempting to hack into the game structure don't even make sense as far as I can see. The game is deliberately and purposefully written so that the player does *not* begin the game with a pre-made party that was assembled in all the particulars before the actual start of the game and its plot progressions. Rather, only two such players are meant to start from scratch while the rest are picked up along the way according to the player's choices.
By attempting to force more than two players into the game from the start, all that has happened is that the situations and choices created later in the game in order to accent and facilitate the player *adding* team members to the party as desired are *nullified.* The mod removes the foundational reasons for the additions of those players, and in the process renders much of the developing game a waste of time and investigative energy.
Further, when acting "alone" in the earlier parts of the game, the starting characters are purposefully subjected to circumstances that, when navigated successfully, contribute to the advancement of the initial players at a rate far in excess of what, say, a beginning party of four members might expect, since the rewards are meant to be divvied up among two members instead of four members. The game is balanced and set up to play through according to its beginning plot structures, and so those are better left alone to avoid with potentially catastrophic game-breaking results, as you have already discovered.
There are plenty of RPGs that allow the player to fully assemble a complete if inexperienced party before the actual adventure begins, and I'd strongly advise playing one of them instead of taking a wonderful game like this and bashing it to pieces trying to get it to follow conventions and plots and rules Original Sin was never intended
Of course, there are no "hard & fast" rules to modding, either...;) You can, if desired, essentially mod any given game to do and be anything other than what it was designed to do and be. At least theoretically. But some changes are simply more logical and more desirable than others, strictly due to the odds greatly favoring the success of the mod taking the course of the least natural resistance to the original game...!...:) For instance, as far as ambitious Original Sin mods go, these two are certainly worthy contenders in terms of making major changes to the game:
1) Modding D:OS to allow the player to start the game with four fully customized party members instead of six;
2) Modding D:OS to support a fully functioning, in-depth day/night cycle.
I believe the second choice above would be the one with actually the best chance of successful completion, chiefly because it seeks to challenge or change *nothing* fundamental about the game, and simply adds to the already-established superstructure of the game itself. I see the first choice above as far more difficult and time consuming because it would necessitate basic changes to the game itself, the ramifications of which would of necessity be felt all the way through the game. The first mod I, personally, would discourage; but the second I would be likely to undertake myself...;)