Wow, your rules are really harsh for non spellcasters. Letting Wizards or (possibly even worse) Clerics come in with all defensive/buffing spells up really makes them overpowered. The thing that makes non-spellcasters powerful is that they are always ready to go, no rounds needed for casting spells.
Suggestions:
Go with potions. They are very cheap compared to your max gold at that level, and you can have just drank all of them. Str/Dex/Con/Wis buffing for sure, also any others you can come up with. A Brooch of Shielding is also a wise investment, as is (if you can afford it)a +5 weapon. Even +5 arrows would do, just something that will ignore Stoneskin. Bumping your saves is probably a good idea, a Cloak of Resistance will do that. Potions of any buffing/defensive spells that might be useful, particularly ones that will last a little longer. Basically, the spellcasters have a huge bonus because of the format, you can even the odds a little by using potions to match whatever spells they can cast on themselves. And hey, if you drink a potion of stoneskin (not sure if it's possible), your DR from it (+5) will technically let you attack others with a DR of +5, even if only with natural weapons. Not sure if that'll work, but it's worth a try.
--Seule