You don't need to use the salt. Someone correct me if I am wrong, but I was under the impression that your plants won't appreciate salt too much. Some people use it as part of their general maintenance, while others just use it for treating ich and as a stress reducer while treating for other diseases. There is no right answer, but just FYI it isn't necessary.
As for the filter, I assume you are talking about the Aquaclear 50 (200 gph). I always find the manufacturer's rating for HOB filters to be pretty overrated. While I would not use that filter on a 50 gallon tank, you may be able to do so on a 35. My only concern would be that you may have one end of your tank that doesn't have much water flow. If you use the Aquaclear, I'd add a small powerhead on the other end of the tank, pointing toward the filter. Or, you could go for the next size up, the AC 70 (300 gph). Or, if funds permit, a canister filter would do a great job for your tank. Then you can have the intake on one side, and the nozzle or spraybar on the other side. No dead spots. Either way, you should be fine.
When you do your PWCs, you don't have to do deep gravel vacs in the areas that are planted. What I do is just kind of rest the gravel vac on top of the substrate in those areas, and suck up whatever detritus is on top.
If you don't already have the tank set up, I recommend Eco Complete plant substrate. It has absolutely worked wonders for me in my discus tank. You can use it alone, or mix it with gravel if you don't want just black substrate.
Good luck with the tank!
