I have downloaded the bitcoin client and the client has synced with the network. I have made a few transactions with my wallet, both inbound and outbound. I have also encrypted my wallet with a password. I have also backed up my wallet, locally, and also emailed it to my gmail account. Two questions...
1. will the wallet address that I have used in the past continue to be mine forever? Or will it change after X number of transactions?
2. If I backed up my wallet 2 months ago, then made several more transactions after the backup, then my PC crashed, then restored from a 2 month old backup, would my restored wallet be 100% exactly the same as the one that crashed? Would I have the transactions that occurred after the backup?
1. Some wallets create new adresses every time you create a transaction. But old adresses are reusable (Note: This is only true for local wallets! Some websites give you other adresses every time!).
When you create a backup of your wallet, you backup the key to the adresses, so it will work only for adresses you have at that time.
Every coin send to this adress is aviable, if you have the key. It doesn't matter when it was sent.
But attention: When you have 2 BTC on your wallet and you send 1 BTC to somewhere, all wallets will send the whole 2 BTC and some (like the bitcoin qt client) will create a new adress for the 1 BTC change (-> you need a new backup or send this to one of the other adresses)!
This is kinda like actual banknotes/coins, you have them in the value that is sent to you and you need to spent it all+receive change back.