I'm no professional either but I'll do my best to help you out. I've spent a considerable amount of time researching and reading up on planted tanks and am currently cultivating my first 20 gallon tank (ever) that seems to be successful with no problems so far. A few things that you need to know before getting into it is that it can get expensive quick (plants are very expensive), time consuming, a mess, and a hassle but if you love you're fish and the idea of plant life, its really worth it.
First of all I strongly recommended reading this guide three or four times and getting a really firm grasp and understanding of it (its Oldfishlady's sticky)- How to: Natural Planted tank
I also recommend going further and reading the following pages where a lot of people asked similar questions. Any questions you have or terms you don't understand you should google. There are a TON of forums out there about planted fish tanks. Simple google searches will yield you tons of results about the same question.
As for the plants, this is what I did-I google'd all the plants in OFL's guide and looked at every single one of them. I wanted to find plants I personally liked (I personally hate the look of all crpyt type plants) and went on to research the different care, planting and needs of each plant accordingly (I've discovered that plants are nearly as needy as betta's -.-). What kind of plants you want and how many is pretty much up to you, just so long as you're not overstocking them. I don't think having more than one floating plant is a very good idea because Betta's need to get to the surface very frequently and they can panic/get scared easy (at least mine does) especially in a smaller 5g tank. My betta has already gotten stuck on my frogbit and I only have 3 bunches of it in my 20g.
As for the order of materials to buy, I started from the ground up; the substrate, the cap (cap refers to what goes over the substrate, mine is pool filter sand), different types of decor (caves, rocks, etc.), the sponge filter, the heater, the tubing (gang valves, anti return valves), the air pump, the plants, the water, snails and finally fish. Since you're tank is only a 5 gallon, I'm unsure if it will have size problems or even need a filter. I'm sure someone with more expertise will chime in soon enough though.
Hope that helps a bit,