Don't try to do everything at once.
- Mount your pickups first. (Are you going to route new pickup holes? Think about routing a battery box space as well).
- Then wire the blend (pan) pot. And see if it is functioning properly. If not there are several forum threads about blend pot wiring, search for them.
- Add your volume pot if you want (maybe a pot with push/pull switch for future preamp bypass function).
Now, you can play your bass while thinking and searching about the preamp.
- When you decide about the circuit, assamble it as 2/3band EQ and see if it does what you want.
- If you still have space in the control cavity think about the additional functions: Mid-freq switch / passive tone / coil split switch for MM pickup / series-parallel switch for P-pickup / Z-mode switch, etc.
Also, see this thread: TB11 Preamp Project