How do I design the passive crossover for a 4-way professional quality speaker?

Here are the drivers:

Tweeter
3 x Mids
Mid bass
Subwoofer

I would like to make a passive crossover for the system the keeps a flat response and doesn’t blow any of the drivers. Any ideas or websites that could help?

I need to know what kind of crossover to use, like what order and what type.

Should I make it a 4-way, or just put the tweeter and mids on the same frequency range?