In Planescape Torment, you're an overpowered DM's pet who completely cheats through the game's systems (at least, if you make the right choice and pick mage).
Baldur's Gate is a PC game for peeps who played 2nd Edition D&D, which is the source you're supposed to learn about stats and classes and terminology and stuff from. Also the miracle that is percentile strength.
Anyways, 10 strength isn't as bad as it could be, you neither have penalties nor bonuses to your melee attacks and damage. THAC0 is an incredibly bizarre way of describing accuracy, but that's just Gygax and Co. for y'all... Basically, it's an acronym. "To Hit Armor Class 0", meaning that in order to hit an enemy with an armor class (AC) of 0, you need to roll (number) or higher on a d20. Since your THAC0 is 25, that means it's physically impossible to hit anything with an AC of 0, since you'd need to roll 25 on a die that only goes from 1 to 20... Or you could just roll 20 and get that automatic success that is a crit.
The relationship between THAC0 and AC is a bit funky to describe, but I'll try. If we consider THAC0 to just be your general accuracy, AC is the number subtracted from the enemy's THAC0. You've got an AC of 10 (really? That's not as bad as I'd thought with the -1 DEX) That means if you were to attack yourself, you'd have to roll (25 - 10) 15 or higher on the d20. Yes, this means that a lower AC is better, and it does indeed go into negatives.
Also yeah, 3 CON is... Fuck, dude. There are cutscenes that could kill you. You could die to cinematography.
I'm pretty sure BG uses the hit dice system though, which means that each time you level up you roll your class hit die (d4, in wizard's case) and then take that number as new hitpoints. This is then modified by your CON mod, which means... Well, it should mean at least -3, if not -4. Which means you'll only be getting 1 hitpoint per level. Not sure why it says "-2 HP per level", there might be special considerations in place. I think selected game difficulty also plays into it.
As an aside, there are no real penalties to picking an evil alignment and then being a good guy. Alignment vs. Reputation conflicts only result in affected party members getting pissy and eventually deserting the party. Since you cannot break ties with yourself and leave your own party, you're stuck with your cognitive dissonance.