1: What happens if I delete my wallet and dont recover it, my bitcoins are lost? This means that , eventually, the 21M Bitcoins can disapear?
The Unites States of America prints money from time to time. But it's won't be the case of Bitcoins, isn't this a problem?
Bitcoins can be lost forever, yes. In that case, all the other Bitcoins in existence go up in value. Since Bitcoins can be divided into .00000001 increments (technically, not currently in the mainstream client), we won't have to worry about running out for a while.
2: I want to make a ''Bank Wallet'' and a ''Small Wallet''
Can I just sent money to my bank wallet without having to worry about it or will I have , one day, to open the client using the Bank Wallet so that it can receive the Bitcoins? I really would like it if I could just crypt my Bank Wallet and recover it only when I feel like withdrawing.
You have to open a client with the bank wallet at least once to create it and get an address. After that, you don't have to keep the client running to receive incoming transactions. You can shut it down and back up that wallet. Then later, when you run the client again with the bank wallet, the transactions will all show up all at once* when you open the client.
*After downloading all the blocks.