Handshake event depends on what you have to buy. Pre-order handshake events costs 1000 yen but for the usual release events, you have to use the event ticket that comes with the CD.
The most popular members during handshake events in my opinion are:
9, 25, 6, 23, 3, 20, 21, 15 (almost always crowded)
19, 16, 14, 12, 24 (short lines)
13, 17, 26, 22 (usually don't even have to line up
)
I have no idea how popular the 5th gen are since I haven't been to any handshake events with them.
I think I'll be going to Umeko, Serina, Asahi, Ruka, and maybe two out of the 5th gen this time. Shame that Amimi and Manami are absent