I have gone to Aquarium Center over the bridge in New Jersey for fish in the past. Not sure about their plants. Any recommendations about where to get plants and plant supplies?
Aquarium center has decent plants. Even petsmart has some good plants, just be sure to inspect them. You could always buy plants from people here on TPT as well. Make sure to choose plants that will do well in lower light levels.
Do you think a short term DIY CO2 infusion would be enough to get started before I get fish in there?
Most fish give off a negligible amount of CO2 so they won't really help in that regard. Whatever CO2 method you choose you will want to stick with it to avoid algae issues and stunting your plants. If you start with DIY CO2 and then stop after a short while then you are cutting the carbon supply that the plants have gotten used to and this could cause them to stunt/melt/die etc. If you didn't want to go pressurized then excel may be an option. You could do DIY excel to keep the cost down for a tank that size. (Buy a gallon of metricide and mix to the correct strength using wet's glut calculator
... ends up costing around $25 for a large supply.) You might be able to get away with no carbon supplementation as well, especially if you have mostly easy going plants.
I have a ton of rocks to build with from a former cichlid tank--want some plants that will grow on rocks if tied to them.
Anubias, java fern, bolbitis, mosses, etc.
I'm also open to recommendations on the best substrate combinations, and the best prices around here.
Some people use mineralized top soil with a sand or gravel cap. Personally, I like seachem flourite black with either a fluorite sand cap or more economically, black diamond blasting sand.