Hello welcome to the deep end.
There is just about endless setup possibilities in planted tanks but if your looking for an easy low tech tank... You've got an excellent start!
The pool filter sand with a gravel cap will work just fine. Check out the the tank journal I did when I set up my 125 in the link on my sig. Builders sand with a pea gravel cap.
You will need to change the bulbs in the light. Let us know the type (T12, T8, T5 etc) and wattage. This will let us know if you have enough light. Retrofitting a hood for higher light if needed is cheap and easy if your like DIY. For replacement lights just look for "Daylight" as the advertised temperature. It's generally between 5-6000K. I'm running 10 - 23W CFL lights over my jungle of a tank.
Fertilizer - Yeah the guy at the store misrepresented the facts. It's much easier than that. Search online for Aquarium fertilizers and order a Macro-Micro mix. You can also order PMDD but will need to buy Phosphate to add into it. I did very well when I was first starting out with these. Just drop the dry ferts into the tank weekly and stir.
Weekly water changes at the beginning just do them. 50% is a nice round excessive number. As you learn more you can reduce the amount down. I'm down to 1 or 2 per month now.
You'll also need a timer for the lights. These are less than $10 at the hardware store.
If you are dosing CO2 you need a canister filter or a sump. If you are not dosing CO2 an HOB works great. I've got three little tanks in the garage with HOB's growing plants like crazy. If you want easy and low maintenance, forget about CO2 for now.
BTW you will grow algae. Accept it now