I bought the claw of kazgorath or whatever at high hedge which decreases con by 2. I have it equipped on Minsc right now so his con is temporarily at 16 from 18. Will his hp gain at level up be reduced from this?
And what items transfer from bg1 to bg2, I read somewhere that the helm of balduran & the claw mentioned above are, anything else?
Your hp bonus from con is retroactive, the moment you lose con you lose all the extra hp from it, same for when you gain.
The only item that transfers (legally) is the golden pantaloons. I recall that when SoA first came out, you could get different items in the prelude based on what items your character had. Like the +2 warhammer Ashdeena instead of the Sword of Chaos. Though I haven't been able to replicate it after the patch (recently did a SOA only full patched run with an imported Fighter/cleric multi). The +2 longsword Varscona was also another.
Though, technically all your gear transfers except for a handful of items have share the same id (some wands, ammo, potions). If you don't mind cheating you can mod the game to not delete your gear or just remove it manually by pausing after the loading screen.