Welcome to the forums Suzanne
I love what you wrote here...
Before I follow any suggestions, I always like to do some research, first
To give yourself the best start and maybe even save you some money on the upgrade of your tank thats the best thing to do.
Listed on this forum are thousands of ideas and setups, the best way to go about it is to find a tank you like and duplicate the equiptment... we have them as simple as you like or as demanding :roll: as you like... hehe
By the way... your LFS is all wet... you do not have to change
from gravel to sand, if the tank is established I would leave it alone, after 7 years you must have a great substrate for plants. If it is coarse gravel you could simply "add" some sand into the tank. By slowly adding it in, it will settle between the gravel without losing any of the precious bacteria or fish mulm for the plants to utilize.
Sand eventually finds its way to the bottom anyhow.
I would just rinse enough to add a 1" layer to the top of the entire substrate and then slowly
mix it into the gravel with my fingers. If you do this carefully you will have minimal mess and a great base for the plants.
7 years is a lot of good nutrients through fish waste... it may surprise you.
Spend on the lights instead.
Any photos of this tank ? I would like to see what you have for gravel... you want about 3 inch depth for plants.