OMG, SH-etc. You are making it sound so difficult. All I did was set up a tank with tap water and added Discus. I read up on all the rules here but mostly I just changed a ton of water until the sponge filters catch up with the bio load. (sometimes a good supplier will give you a cycled filter free if you need one.) I will answer your questions that I can answer according to I have learned over the years.
Water change every day, at least 30% in a BB tank. I want my nitrate at 5. Some folks say 10, but I disagree.
I keep mine at 82 and they are comfortable with that. If you want your electric bill to be more, there is nothing wrong with 84.5
Any pH is fine as long as the incoming water is within .4 pH as the water in the tank. If you have a greater pH swing you will need to age the water before you introduce it to the tank. You can find out what your pH swing is by putting an air stone in a bucket and add straight tap water, let it bubble for 12 hrs and check to see if the pH of the aged water is the same pH as your water straight from the tap. Or you can do what I did and use tap and watch the fish for 6 or 8 weeks and see if they start acting less happy. If you watch the fish they will tell you if something is wrong.
Don't mess with your pH. Ph will go lower in an established tank if it isn't getting adequate WC. Otherwise it should be stable.
TDS and kH only matter if you want to breed.
Beef heart is dirty so you will have to feel like doing more WC. It does make young fish grow so it's a trade off. What I feed is pellets twice a day and freeze dried tubifex once daily. Most people here thing that tubifex is a no no but I disagree.
I already answered question number 5.
I rinse my sponge filters in a tub of dechlorinated water when they are filthy.
How you do what is necessary depends on your set up.
This is the best I can do. Any more questions?