Yeah, the caster level thing is complicated. The sublime chord PrC can cast 4th and 5th level spells with a caster level of 2 with the right build (not even using mage slayer or other feats). This can easily be extended to 1st through 3rd level spells as well with the extra slot feat. Similarly Ur-priests and other classes can cast higher level spells with a reduced caster level compared to a wizard or cleric. You might want to point out that these tricks (especially an artificer copying their spell casting for crafting
) are considered broken by some on the boards, it does not seem fair that the reverse is fine to enforce.
What books do you have access too? If you are mainly interested in healing potions, maybe you should drop the brew potion feat and pick up craft wonderous item earlier. The belt of Healing on page 110 of the Magic item compendium lets you heal 2d8 points of damage 3 times a day for 750gp. Now you need cure moderate wounds, so you might not have access to it until level 8, not so good. Another option would be to pick up leadership feat at level 6. You are suppost to be raiding other paladin orders and it is a solo game, why not get some foot soldiers. While you are at it, maybe you can get a cohort cleric that stays at home and crafts potions and other things. Being a cohort, the cleric will get XP based on how much you get without ever leaving home. And if the cleric is not in the actual battles, it won't interfer with your DM's style.
Your best bet though is just talking to the DM. If you are the only player and the potion brewing rules is the main thing holding you back (which is minor in my book compared to the rest of the stuff you put up with), the DM should give you a break. Making the one PC in the game of minimal effect makes me think the game is being run incorrectly. If nothing else, go Greyguard later and start eating children while maintaining your paladin abilities to express your displeasure.