Soo.. Your minotaur class gets ALL of his attribute bonuses at start game?
Yeah. He has a net -2, not counting Strength. And, as mentioned, the combat applications of his Strength do not apply right off the bat. You seem hesitant with the "Soo...", but I don't see why. His Strength, for purposes of combat, would be no different than any other character.
What do you do if the Minotaur's player wants his first level to be in Barbarian/Fighter (instead of his first level in Minotaur)? (This is the reason for a basic Race, before Racial Class Levels.)
If he wants his first class level to be Barbarian or Fighter, fine. He can take it after taking 6 Minotaur levels and getting his 7th character level.
Your language seems like you don't like this idea much. Yet, it neatly does away with Level Adjustment altogether. Having the character take mandatory levels in "Minotaur" is a pretty small price to pay for being able to play a Minotaur at all without all the crap that comes with level adjustment and racial HD.
With 6 racial HD and an LA +2, you're playing an 8th level character as a straight out of the MM Minotaur, or 9th, if you give him that one class level. With mine, the Minotaur can be played as early as 1st level, and can start taking class levels at 7th instead of 9th, and its still the same monster.
Plus, it is at a comparable power level to any other 1st level race/class combination. Its powerful charge (2d6) is about the same as sneak attacking with a short sword (1d6+1d6), but is much more limited in scope and frequency of use. It gains a HD at each level, so you don't need to dumb down the race and play it as a 3rd level character (1 class level + 2LA) with only 1 HD.
Have you thought about balance if the character took one or two levels of the Minotaur Class and then just took Regular Classes? Would they be overpowered from how you frontloaded the ability scores?
Yes, I thought about "balance" by making the character take all 6 levels BEFORE class levels, and that neatly avoids that problem.
The ability scores are front loaded, but actually getting their full benefit is not. Let's say its allowed to "dip" into this class. They do it for 2 levels. Are ability scores frontloaded? Only as much as they are for any other race like Dwarf, Elf, Drow, Halfling, etc.
They would have a -6 to mental stats (-4 Int, -2 Cha), and a +6 effective bonus to physical stats (+4 Con, +2 (effective) Str). That's a total +0 overall modifier. While their racial +8 to Str is reflected in ability checks, skill checks, and carrying capacity, this is as much a reflection of their size; they still only get to use +2 of the +8 bonus for combat. I wouldn't call that overpowered at all. Plus, their powerful charge is doing roughly half damage, they don't get their full Str bonus to combat, their natural armor is not at its best, they don't have their natural cunning or their reach either.
I don't see how its not fair ("fair" seems a better term than "balance" to me).