Transferring clients won't be affected. When the forms are released and you later open a  previously transferred client the updated forms will all show at that time, at least that's how it worked in the past for me.

I generally transfer at least 1, (usually my own) just to play with and see what is there and working.

I don't bulk transfer for the actual returns in any case - My practice has to been to transfer them over as the client information is received. - One of the ways I use to track who is in and who is not.