For first question, you need to supply the time you want to recover to. For example:

run {
set until time '24-APR-2001:09:00:00';
allocate channel ch1 type disk;
allocate channel ch2 type disk;
restore database;
recover database;
};

Second question:
I usually use two channels. I see some others use up to 7 channels. I think it all depends on your system resource. hope it helps


Dragon