So the wallet.dat contains puplic/private keys, transactions, and the block count where it got all previous transactions ?
Yes, since 0.3.21.
If i didnt use a wallet for some time, it will rescan the blockchain i got on my disk without downloading it again? Is there any status shown on the client which tells me if the wallet is up to date with the blockchain dat files?
Yes, it will. It does this rescan automatically at startup, so there is no feedback in the GUI - when it is loaded, the wallet should always be up-to-date with the block chain.