Welcome to the forum, and planted tanks! I too am pretty new to all this and had asked similar questions.
1. I think it will be plenty of light for moderate plants. with the 84w you have about 2.8w/ gallon.
2. I would think the filter would be fine especially if you keep up with the WCs. some people feel that the bio wheel will be harmful to the plants but I havent seen any real proof of that and I personally really like the emperor filters.
3. I didnt buffer my water at all, I took mine right from the tap to the tank.
4. This one I dont really know the answer to. Sorry
5. Havent had any experience with it. Im using DIY yeast.
6. I think it comes down to preference I like the open top look better but I cant do it because my cat would make a smiwwing pool of my tank.
7. I added my plants the day I set the tank up. and added fish the following day.
I hope I was of some help and Im sure your questions will be answered shortly by some of the more experienced members here.
once again welcome