Suikoden II is about twice as long as Suikoden. If you do plan on playing them in order, it'll be a while before you get to lucky number V. In case you're wondering, my final run times for the games were:
Suikoden ~ 20 hours
Suikoden II ~ 40 hours
Suikoden III ~ 40 hours
Suikoden IV ~ I stopped playing at 10 hours because it's awful
Suikoden V ~ 55 hours
I never bothered to finish Teirkreis for the same reason as IV, but your mileage with it (and IV) might vary.
Either way, enjoy. It's a great series.