Help with Space Setting [SF]

[myrmidon]

I am running a fairly conservative sci-fi campaign, with humans at TL 10. They just encountered an alien species, at TL 11, and are heading to visit their home planet. I am struggling with two things, one about the home planet and one about the aliens. I (mostly) randomly generated the aliens, and have the basic stats from the planet from when I generated the aliens (atmosphere and gravity). I like having dice determine story elements. It gives the game extra excitement and unpredictability, even for me as a GM.

1) First question: the planet. The aliens are an ammonia-based life form, so I have assumed that the planet has an ammonia atmosphere. Is that necessary for an ammonia-based lifeform? There are brief descriptions of ammonia-based planets on S82 and ammonia-based lifeforms on S138-139. But I am having trouble what the planet would actually look like, as in, how would it appear to our senses? What does it look like? It is generally mountainous, but what does the dirt and rock look like? Does the ammonia cause discoloration? What do the indigenous plant life look like? It's probably not green. I am mainly looking for help in visualizing it for myself so that I can describe it well to my players.

2) Second question: the aliens. The aliens were randomly generated as a tri-axial lifeform. I have been able to imagine, draw, and describe that to my players. I have been able to justify it so far in my mind because they live in a mountainous area and clamber about a lot, and it helps to have all kinds of extra manipulators to climb and hunt. But I have been struggling with if that would actually occur. Generally, life is fairly optimized for its environment. And, in gravity, two sides is much more efficient than three. How would three sides develop in gravity? They have already been introduced, so they can't be ret-conned now, but I thought it would be helpful to discuss.