Hello Kevin,
Welcome to TFF! Can I offer a suggestion first? I have pretty bad eyes and I had to struggle quite a bit to read your post. If you could darken your font just a bit, that will help. Otherwise, your may get less responses if your post is difficult to read. I have the Blue skin on the Forum, and Blue on Blue looks aweful.
Regarding your question, I personally use a very fine grain (1-3mm) natural gravel substrate mixed in with Laterite which is an iron-rich substrate that absorbs nutrients quite well. There are, however, loads upon loads of different substrates to use that will benefit your plants and are safe for fish.
A 4ft tank sounds like a great future project. Though, substrate is important, lighting is by far the most important component of a planted aquarium. We have a planted section in this forum that you may want to visit. All types of planted aquariums are represented from high-tech to low-tech practices.
To get you started and give some inspiration, I'm giving you the following link to a pinned topic that features members tanks. In each submission, members give details about their substrate, lighting, plants, etc.
http
/www.fishforums.net/index.php?showtopic=111385
In addition, if you click on the links in my signature, they'll take you to four journals of my planted tanks. My nitch is low-light, low-tech, low-cost setups that are still pleasing to look at. I also have a link to a list of easy to care for plants. The methods I use are not the best nor are they only way to have a successful planted tank, but because I'm not made of money, they tend to be more cost effective and less complicated than some of the other methods in this forum.
Good luck to you,
llj