auxilary fuse box

I tried searching on this subject not much luck.
Adding a lot of electrical items to my 71' dart.
thought it would be easier to mount a auxilary for the items so it would not tax the existing electrical system.
Just an idea,I'm not an electrical guy.
adding:
fuel pump
electric fans
electric water pump

this an logical idea? this way I could wire seperatly to the battery with a relay.