Start with what you need. One Stompblox can fit 4-6 pedals.
Two Stompblox can fit double that. Obvs.
Add Extend to attach a power supply & add 4 more pedals.
Check out the Stompblox modular pedal board demo by Pro Guitar Shop’s Andy Martin!
Since Stompblox are modular you can make your pedalboard any size you need. What is the most common? Here is a good starting point:
BASS PLAYERS: Bass players typically get 1 Stompblox and often an Extend. This allows you to mount around 5-6 mixed size pedals (including a wah) and a power supply on your pedal board.
GUITAR PLAYERS: Guitar players typically have more effects than bass players so its hard to say what is typical. The most popular configuration is 2 Stompblox and 2 Extends. This allows you to mount your power supply and around 14-16 mixed sized pedals and an expression or wah pedal on your pedal board.