How much water to put in my pasta pot?
The pot choice should depend on the amount of water (which depends on the amount of pasta you're cooking) rather than the other way around. For detailed advice on amounts, see these answers (answer 1,  answer 2).

Generally (not using fresh pasta or very long pasta when more water is necessary) you just need to cover the pasta. A bit of oil on top will help keep it from boiling over, as will keeping the lid off after it's begun boiling and just simmering it rather than a rolling boil.

With longer pastas like spaghetti you should add more water than just enough to cover the pasta, but as long as the top of the water is more than an inch below the top of the pot (after adding the pasta) you shouldn't have trouble if you follow the precautions above.