If you want to give environmental description, I usually add little tone setters. What does it smell like, is there a sound, a breeze, is it warm, etc. Just add one or two of these quick and that should help give detail without spending too much time.
I try to do the same with a lot of things, give enough information to give the reader an image to work off of, but not so much as to take too long. I only give extensive details when describing important characters or writing action scenes. But when writing said action scenes, I don't explain the characters' abilities and so on. I instead try to let the action be the exposition of the characters and what they can do.
As for pacing, novels have a 15K character cap, so if we split the story into AKTs, you'd want each akt to be around 5K. Not something you have to do of course, its more just measure the amount of time in the editing process, then think about whether you've done good in establishing and completely different things
