When defining my CO ranges; Flat vs EP, Flat vs MP and Flat vs EP+MP. I ended up with some doubts about how these ranges should look like.

Mainly I have a poor understanding of how my range should be affected when there is more than 1 player into the pot before me.

Like we get better odds but at the same time our equity goes down the hill. How should I consider this appropriately into constructing my range, any thoughts?

Depends on the type of hand you hold. For example vs a raise MP, CO call, and you're on the button:

K9s with deep stacks, I'll call this. Short stacks? Depends on how bad my opponents are, probably folding without reads.

76s, with deep stacks, I'll call this. Short stacks? Definitely folding.

ATo, with deep stacks, I'll fold this. Short stacks? Depends on what I think of the opener; sometimes shoving but usually folding.

88, with deep stacks, I'll call this. Short stacks? Depends what I think of the opener, either shoving or calling depending on that.

-----

Contrast all that with how I'd play those hands vs just an open raiser:

K9s: easy fold imo.
76s: easy fold imo.
ATo: easy fold imo.
88: 3 bet or call.

Why is it different? Because as players enter the pot, implied odds go up.

In theory, do less flatting in position (you're opening yourself up to a squeeze you can't call, and you have less chance of winning multiway when you have the weakest range). Do more flatting in the BB (you close the action and have sick pot odds, so it doesn't matter that you'll lose pretty often). In position (and in the SB), you should be squeezing pretty often yourself. You don't make much money by pressing "CALL" pre-flop.

In practice for soft games, the game is usually fishy if there are multiple callers, and seeing a flop with a fish in the pot can be very +EV.