I need some one with experience to answer this.
Is this set up going to work and sound good?

guitar ---> stompboxes (tuner, big muff) ----> interface (w/ a midi foot controller plugged into the midi input) ---> macbook pro (w/ logic express) -----> amp.

Is the combination of logic express with a midi foot controller controller a good idea to use as sort of a virtual digital multi-fx unit? or is this difficult and awful sounding?

and do I need speaker cable to connect the interface to the amp input?
my band is here ------> myspace.com/weareattica
There's a way of doing it... I think on the 'real' set ups (as in designed for this application) use loops to run the stompboxes, and then you might actual want to run some of the effects through your amps effects loop. It hard to really say how to connect everything without seeing it though.

And no you don't need a speaker cable to go to your amps input... just make sure you're still connecting your amp to a speaker though.
I have a huge fear if rays.
by fx do you mean stompboxes, or the interface/laptop thing?
my band is here ------> myspace.com/weareattica