[Space] Interactions between species

[Frost]

I am looking at running a campaign that is more or less stock space opera (ok with a bit of a hard SF undertone- it's still me) but with exclusively non humanoid, if not full on starfish, aliens.

While I am still at a very early stage so I don't know the species I want to use I am trying to figure out how the fundamentals will work and would appreciate any experience or ideas you have.

My big questions are:

How do these species interact?

I am assuming that for the sake of my sanity that all my species are going to have carbon/ water chemistry and breathe oxygen but that still leaves room for a lot of conflicting needs. How are environments organised to meet the needs of more than one species?

How do I handle equipment?

I know there are rules for differing sizes for armour suits and other life support items but how best to handle (or even describe) gear for species with different manipulators has me stumped.

Thanks in advance.