Welcome to Aquaria Central. I'd also like to personally welcome you to the plant section of this board! =D You'll find that once you get a good hold onto plants, there's no turning back! =)
Looks like you got a decent start on your lighting. Two 96watt CF lights will do great on a 75 gallon tank. There are a few things you need to consider however. With that much lighting going through your tank, you must consider getting a CO2 system for your tank. DIY CO2 can work, but it will take a considerable amount of effort to maintain (think 5-6 bottles per 1-2 weeks depending on recipi). For any tank larger than 30 gallons, I would suggest getting (or building your own) pressurized system. My 70 gallon tank has 4x55watt of CF lighting over it, and a 5 pound tank of CO2. I'm able to keep about 20-25ppm of CO2 in the water column, and my 5 pound tank lasts for 6 months. Refills only cost me 10 bucks Canadian. IMO, its well worth the initial costs of setup. I won't get into the details of a CO2 system, for you can probably go back into older posts to look for more info.... but if you have any additional questions, don't hesitate to ask.
As for your substrate. Plain gravel will do fine, but initially, you may need to supplement the gravel with plant tabs. Of course, this entirely depends on whether or not your plants are heavy/moderate root feeders, or water column feeders. Personally, when it comes to plant substrates, I like to use a substrate called "Flourite," which is made by Seachem. I find it to be a very good substrate. If you are not willing to completely replace your substrate, you can mix the flourite into your gravel bed. You want to achieve a depth of at least 4 inches for a good plant substrate. A 50/50 mix of flourite and gravel should do fine... but a lot of people find that a 100% flourite substrate does best.
For your plant questions... I have no experiences with mail order plants and whatnot (being in a northern Canadian city doesn't make it easy to order stuff), so I'll leave that to the others. As for what kind of plants to get, what exactly are you looking for? Do you want a tank that has fast plant growth, or slower plant growth? What kind of colours are you looking for? A lot of it involves your own personal tastes. Don't ask for me for design hints and tips... I can grow my plants nicely, but I can't aquascape to save my own butt.
One thing I will mention though. When you start your tank, before you turn on your lights, or plant your plants, make sure you have a good and stable concentration of CO2. This
table is a good place to start. After you are sure you can keep the CO2 levels constant, pack your tank with as many fast growing plants as you can get. Turn on your lights, and run your filter(s). After a day of allowing your plants to settle in, get your herbivores (ie. algae eaters). C. japonica (amano) shrimp, SAEs, ottos, etc. will do fine. Make sure you keep the bioload very light at this point, keep a very close eye on ammonia levels. If done right, you shouldn't see any indications of ammonia, as the bacterial colonies present on your plants and the plants themselves should take care of any ammonia your herbivores can produce.
Allow your tank to further settle in, prune your plants if they are overgrown, you can sell your clippings to your LFS for store credit if you want. Just make sure your plants still take up a very large majority of your tank. After a month, you can begin to very very slowly introduce your main show fish into your tank. Keep a very close eye on your ammonia readings. Again, if done right, you shouldn't see any indication of ammonia on your tests.
After you've completed the addition of your fish, let your tank to settle in for another month, then slowly remove your plants and plant other plants in their place. Over the course of a few months, you can slowly remove the fast growing plants and put in slower growing plants instead... which will reduce the amount of maintainence time that you'll spend on your plant tank. During this period, make sure you don't remove too many plants, or you may cause a small ammonia spike. You don't want to see ammonia in a plant tank (or in any tank with fish for that matter).
Don't worry about throwing out those plants that you bought in the beginning... you can bring them back to your LFS for store credit (or however they pay you back). Use that credit to buy different plants for your tank. It works out quite well.
Thats one way of setting up a plant tank.
Other people do a fishless cycle on an empty tank. After the fishless cycle they plant their tanks and immediately add in all the fish that they were planning to get. This works too, but you'll spend a week or two staring at an empty tank. I personally like the longer method.
Remember one thing... keep ammonia levels as low as possible (0 is preferred). Even a small ammonia spike can lead to an algae outbreak... and I know that a lot of people (including me) hate fixing that kind of problem.
If you have any more questions, please don't hesitate to ask... I might have missed something important.
HTH
-Richer