Here are a few more observations about buying tickets and attending baseball games.
1. When you reserve the tickets on 7ticket.jp, you don't actually need to print out the voucher to collect the tickets and complete the purchase at a 7-11. You can just show the cashier the voucher on your phone and they will scan the bar code or type in the transaction number. 7-11 charges a fee of 108 yen per ticket.
2. I think for 4 of the 5 tickets I reserved online, it gave me until midnight the following day to purchase and collect the ticket, but the last ticket I bought for a Fukuoka Hawks game in September it gave me 3 days to collect. Not sure why, maybe that's the Hawks policy, maybe it's because the game is more than a month away.
3. The only downsides I see to using the 7ticket.jp system are the annoying Japanese CAPTCHA and the fact that you can't purchase tickets weeks/months in advance of the game if you're not in Japan. However, I've heard that Yomiuri Giants and Hanshin Tigers games are the ones that sell out the most, and you can buy those direct from the teams' websites.
4. I've read a lot about how the home fans sit on side of home dugout in Japan, and visitors sit on other side. Most teams have home dugout on first base side, some on third base side. My observation is that this only matters if you want to sit in the bleachers in the "cheer section" or "ouendan." The visiting team cheer section "Ouendan" is in the outfield bleachers on the side of the visitor dugout, the home "ouendan" is in the opposite outfield bleachers. All the other seats are more or less filled by home team fans.