I have a pretty large system, 47 dutch buckets, a flood and drain table and a NFT with 36 sites and I use that master blend with everything its good stuff. You can get 20 pounds of epsom salt on amazon for 30 and the 25 of calcium nitrate on amazon for $30. This depends how much you are doing though a smaller kit may be a better option.
I would get the 12.5 or 25pound if just starting out. Don't get the 2.5 pound