Some of the dedicated plant keepers use specialised substrates, sand is only good for a few plants like some of the spreading vals, I use a fine-medium gravel and plant mosts rooted plants in small pots set into the gravel.
depends on what fish you want to keep (diggers or not). Generally, plants like sand better. There is some discussion about play sand (check out old posts in the Setup forum), but I have used it forever and it works great. It has just the right grain size. Remember to get some fertilizer (laterite), which you mix with the bottom third of your sand. Then add the remaining 2/3 of sand.