Thanks Oni, this is a great topic. I hope the following makes sense. I am just spouting some thoughts based on what I know about this planet.
If I had to bet on the biochemistry of extraterrestrial life, my money would be on that some of the basic processes of terrestrial life would be common. Things like photosynthesis, glycolysis, etc.
I say this based on a few assumptions. One being that that Earth is 'ordinary'. That is, the early history of a planet in the ballpark of Earth's size and position around any remotely similar star will be more similar than dissimilar to our own history. If this is correct then it is not a complete leap to assume that at some stage in that planet's development abiotic carbohydrates and other critical components of terrestrial biochemistry (such as adenine) were abundant.
While it is fun to speculate about different biochemistries, given how readily some of the building blocks of terrestrial biochemistry have been shown to form suggests to me that we should expect to see them elsewhere. What I mean is that while carbohydrates do not have to be the basic energy source for life, it would seem strange to me for it not to be the most common one given the abundance of such.
So if that is the case, then glycolysis is likely to be common, and if that is the case, then photosynthesis (and/or chemosynthesis) should also be common as they are remarkebly similar chemical pathways (just in reverse).
From there, using Earth as a model, I would guess that the vast majority of life in the Universe are analogs of our prokaryotes (yes I know that this applies to Earth as well!). As I understand it prokaryotic life, including photosynthesizers, appeared on Earth just about as soon as they were able to exist. Then they just existed for billions of years. That suggests that from a probability standpoint life is easy to make, eukaryotic life on the other hand is tough and unlikely. So probably a lot more extraterrestrial stromatolites than green-skinned Orion slave girls.
Doctor Bashir: "Of all the stories you told me, which were true and which weren't?" Elim Garak: "My dear Doctor, they're all true" Doctor Bashir: "Even the lies?" Elim Garak: "Especially the lies"