I haven't played the PC version myself so I can't say too much about the mods, although I do know that unlocking the framerate really

s with the collision detection so you will probably want to stick to changing the resolution only.
"Classes" don't matter as they only affect starting stats and equipment, none of which is all that important. Still, I'll vouch for the pyromancer as a beginner class - the fireball spell is decently useful and you can learn more if you want to, and their low starting level means you have slightly more wiggle room with your level-ups.
As a big Souls fan who also sucks at the game mechanically (I've gotten better, but yeah...) my advice for enjoying the game is to familiarize yourself with how the stats work, and what all the symbols on the inventory and status screens actually mean. What stats you should aim for largely depends on your build and especially what type of weapons / spells you plan to use. Depending on the equipment, it can be best to have high strength, dex, int, or faith, or some mix thereof.
Here's a decent little guide. Endurance is also important so you can equip heavier gear and still roll effectively.
That said, Dark Souls *is* an action game, so even if you utterly fail at spec-ing it's still possible to brute force one's way through.
As for humanity, it's pretty simple, really. You can use it to become human, which lets you summon allies or invade other players. If you kindle a bonfire, that bonfire will then recharge your Estus Flask (healing item) to 10 uses instead of the usual 5. It has a couple of other obscure uses/effects but that's all you really need to know. Read more
here.
Other advice for your first real playthrough:
- Find a shield that absorbs 100% of damage ASAP! (Or at least 85%+)
- Get a bow and some arrows, even if you aren't specializing in Dex, they are really useful for drawing aggro or killing weak enemies at a distance.
- As mentioned above - make sure your equip load is low enough that you can roll effectively.
- Avoid fighting multiple enemies at once at all costs.
- Play with a gamepad. A 360 controller is acceptable but feels way off in my opinion compared to a Dualshock 3.
- Don't be afraid to use cheap tactics or do whatever it takes to survive. The game sure isn't above such things.
Oh, and the game should be converting to Steamworks in November so you might want to wait for that.