Depends on their home world, I would say.
They could be humanoids, if for some reason the evolution of their species has seen it necessary to turn bacteria into humanoids. Then it would depend on their athmosphere whether they breath oxygen or some still unknown substance. (Anti-oxygen perhaps?)
But it's hard to say - I'm no scientist yet, so I can barely make vague ideas on how they would look when the conditions are X and Y. In my imagination I say the Asari come pretty close to what I'd expect in terms of looks. Perhaps the Salarians too. I'm not so sure about the whole 'everything is connected' part though. Allthough 'Embrace Eternity' is a cool phrase.
Quite possibly there are quite a few different species out there, some looking like the others, some being completley different. (Elcor anyone?) Hell, it could even possible there is even another human species out there. Who knows?
Imagining is fun though, so I'll throw something off the top of my hat.
Skin/protective outer layer colour: brown/grey
One head, two eyes, one in front, one in the back.
Walks on four legs, has 2 arms.
Talks the same way we do.
Can't smell. No nose.
Gets nutrients by absorbing them through their skin. Nutrients are found in the air. Does not need to 'breath', as it also absorbs nitrogen 'their oxygen'.
They are intelligent in the form of having come up with some basic tech. Perhaps have created their counterpart of our computer.
Peaceloving. Only minor quarrels between themselves. They live as one, there are no nationalities.
The average adult is about 2 meters high, 3 meters long. Average weight is about 200 kilograms. Whole organism is carbon based.
'Men and women' counterparts exist. Breeding is done in a similar way. (Just because I don't want to think too much about that)
There's some basic information. I think I'll call them "Kurrtuks" and they live on the planet "Tyruhal"