#1
what exactly does a compression sustainer, phase shifter, EQ pedal and an octave pedal actually do?

I've never actually known myself....
#2
i have bosses compressor sustainer and as far as i know the compressor sort of evens out the sound of the guitar in that if u hit a note quietly it will boost it and soften notes hit 2 hard and the sustainer sustains the note making it ring for longer.

...i think

ps the compressor sounds gd with a wah pedal gives a really sort of clipped funky wah
#3
An octave pedal creates a new signal one or two octaves below the original signal.

An EQ pedal can boost or cut different frequencies to shape your tone.

A compressor/sustainer is hard to describe. It sorta 'evens out' your tone. Basically it's good for that really really clean sound.

I think a phase shifter is the same as a phaser...but I'm not sure. What a phaser does is it varies the tone in a cycle. So the tone gets brighter, then darker in this wave-like pattern

Hope that helps