yes, absolutely you can use the word clock out from the V3 (assuming it's not an opti-mod V3). I never di that, because I never bothered to get BNC > RCA adapters or a BNC to BNC digital cable. but I already had an AES > coax adapter, so that's what I used to do.
of course, if you go word clock out of the V3 to word clock in on the HD-P2, you would choose "word clock" for the HD-P2 settings, and not the S/PDIF.
Most V3s have a WC out on them (unless they are opti-moded).
So technically you can do 6ch with the V3 as your master. (AES>coax cable, coax out, and V3 WC out)
If the P2 has bit-clock perfect coax-out, then you might be able to milk another 2 channels and diasy-chain another recorder off of it (or split the signal at the V3 off of the AES out).
Would you use a BNC cable for that?
Yes you can daisy chain P2's.
yes, both the S/PDIF input and the S/PDIF output on the HD-P2 are bit-perfect. So you could use the S/PDIF out from one HD-P2 and send it to another to use as the clock source for the 2nd HD-P2. I've done this in the past as well.
all this HD-P2 sync'ing talk has really reminded me what a great deck the HD-P2 is. It really gives you a lot of options to work with, more than most decks in this price range do.