From what's been said on here, the Sansamp does a rather good Ampeg sound.
The Big Muff is a popular pedal with a lot of bassists (& guitarists). Dirt is kind of a form of compression on the sound, so compressing it further with the compressor set high is gonna completely change the sound. There's a lot of good dirt pedals out there, have a look a some of the threads on here.
I couldn't advise you on a compressor as I don't use one, but there's no correct place for any pedal order, just what you like. I leave compression to the sound engineer to decide if it's needed.
Best advice I can give is to try things out & use your ears. Have fun.