First of all, welcome on aboard...
Don't use gravel which is really, really small. Roots of plants need sufficient nutrition and if the gravel is too small, you'll have a severe problem at a certain point. Everything from 1mm and up would be okay to use.
All of my 60 tanks are planted and the vegetation are growing just fine. In case they need a small boost, I only add carbonized sparkling water (without any sweetening) which you're able to buy at any drugstore/supermarket. I don't add any commercial supplements to these tanks.
Thusfar, I've never ordered plants online. Simply because I like to see a plant for real which I like to purchase. But that's just a personal preference.
I myself dislike plastic plants in a fishtank. To me a fishtank should look natural. So, that means also the plants... But again, also that's a personal preference.
Take care, "S"
Devoted aquarist ever since early 1970's...
Specialized in livebearers &
specific breeder of rare livebearers...