don't buy any products yet. I had a tank for almost a full year and did NOTHING but water changes. Didn't any dosing of chemicals or buffers.
If your good with your weekly water changes your be fine. Your salt mix is replenishing a lot of what you need.
Save your money for now. If and when you start corals them maybe down the road you may look into something. Buffers shouldn't be needed with proper flow, surface agitation etc. again... Save your money.
Purigen or phosguard are good but if your having phosphate issues some products will just mask the issue at hand. I'm a firm believer in less is more.
The less crap you throw in to your tank the better.
Just my opinion.