2) in the meanwhile, that tiny btc amount is someway freezed? Am I able to spend them again (i.e. to use them from the same "unspent output" I picked them in order to build a new transaction)? Or they already belong to the new address and I will be able to spend them only from that new address and only if and when the transaction will be confirmed?
Not until some time has passed and nodes drop it out from their memory pools. Otherwise they won't accept another transaction that spends the same outputs and they will not relay it further. You can of course try until it succeeds.
Most wallet software will continue to try submitting the transaction to the network, so it would not simply disappear from memory pools.