Lots of great questions -
1. Yes, you have the correct amount for directly dosing dry ferts in a low tech setup.
2. There are two ways in which you can dose the nutrients, by making stock solutions or by adding dry powders using a set of standard spoons. You already have the correct calculations for just dumping the dry ferts in your tank with spoons. Or you can make new calculations for mixing the Macros in a 250 ml or 500 ml bottle by downloading this - http://web.archive.org/web/200806010...t_aquacalc.htm
3. KN03 and KH2Po4 can be combined as a Macro solution if you mix them like I mentioned above. Traces or Micro solution can be mixed with GH. Honestly, you can just keep using Flourish for your Micro solution, it has everything you need for trace nutrients.
4. Yes, keep adding Excel for more growth.
5. Many people on the forum buy ferts from here - Aquarium Plant Fertilizer | Green Leaf Aquariums
I find it is easier to make my own solution and dose per ML with a syringe. This way I am dosing my Macros together and 1 less task for the hobby
If you need help calculating your own solution let me know - Good Luck!!!