Does the total number of bitcoins affect the price you are willing to pay for them?
Yes the amount is the amount that have been found (ie. mined). Right now that amount is about 6.5-7 million. The final amount is 21 million coins, but this amount won't ever be reached. Yes, when someone mines a block they get 50 NEW bitcoins. If bitcoins are, "lost" then they are gone forever. Well they aren't lost, they are just in a wallet that will never be spent/traded. Therefor you can say that the total amount is the total amount of bitcoins that have been mined MINUS the amount that have been lost.
Nope. The price is entirely dictated by buyers and sellers negotiating (indirectly) what they are willing to sell for and what they willing to buy for. Its the supply and demand for the bitcoins on the exchanges that dictate the price.