Yay! Another kuhli lover! ^-^ I'm glad I could help! We'll have to share pictures of our kuhlis we we're both done. I also have a slightly higher pH. Driftwood and oak leaves do a great job at bringing it down. I haven't tried peat moss yet, but before I get my cardinals I will.
All of the choices I listed for you would be great and very pretty. Cardinals are my favorite (I'm also lucky enough to have very soft water). I would try to find wild-caught ones as they are actually sustainably harvested and look much better than tank-bred ones, but I would let the tank age a little bit and the pH drop around 6 before you add them. If you have a large enough tank (75 gal and up I think) you could try for discus. I have very similar water to yours and will be stocking my planted 29 gal tank with 10 kuhli loaches, 10 cardinal tetra, and a thick lips gourami.
Ohh!! You've got some good choices! Do you know the exact GH and KH values? Also what size tank? Cardinal tetra are the ones that pop to mind right away, but they need GH and KH values under 4 which is why it would be helpful to know the exact numbers. Discus also thrive in this type of water but are very high maintenance. Rummynose tetra are another good option if it's a larger tank. They school really tightly and look stunning in groups bigger than 10. Mosquito rasbora will also do well if there is nothing in the tank to eat the little guys.
You can do it either way....I like to add the sand then plant......especially for the rosette type plants so that you don't plant them too deep-you want to keep their crown above the substrate...Stem plants it doesn't matter how deep-but you do want to try and keep as many of the lower leaves out of the substrate as you can.
In a recent thread, your advice on cycling includes:
"You need to boost the ammonia levels to around 5ppm..."
I know that's a typo so I hesitate to mention it in public. Still, you may want to clarify or fix it.