I'm thinking of building a rack so I want to know what are the basic essentials I need and in what order the should be connected in
(One for recording and 1 for live thanx)
that's a super vague question....

you need whatever you use

like, really. I have absolutely no idea what to suggest. what kind of music do you play? what sort of effects does your style use or need? what's your budget? do you actually want to build units, or are you talking about putting regular rackmount units into a rack?