Re that bottle number two for nitrate. The problem is the dissolved solids in the solution tend to come out and they simk to the bottom of the bottle. So, not only do we need to shake it like crazy, but is also help tp bang the bottle on a sold sureface a few times during shaning in order to help dislodge the silids abd help get them completely mixed back in.
Despite that, the nitrate test is not the most accurate and where it tends to be off by the most is between 0 and 20 ppm readings.
Any bacterial starter that needs to be added more than once is probably a waste of money.
Qith that much water and that few fish it is going to take months to stock the tank. You should not increase the bio-load by much more than 1/3 at a go to be safe. it take the ammonia bacteroa about 8 hours to double under optimal conditions, its take a few hours longer for the nitrite ones. Thsi si one of the secondary downsides to doing a fish-in cycle. Also the rfrequent testing and occasional need to change water.
I have maintained a lot of tanks, both planted and not so for some time. I tend to be an over stocker, expecially in the pleco breeding tanks. Under normal curcumstances I change water in all tanks weekly toi the tune of about 60%. When I get a new tank I measure from about 1/4 inch above the start of rgwtop frame to about 1/2 inch below the start of the bottom frame. I make a mark somewhere I can see it at the halfway point.
When I remove water it is to that mark. Because of the decor that remains submerged, I know there is less water left than I took out. I estimate it is about 10-15% more than half of the total volume. So i am doing about a 60% or a tad more change. To date i have never heard a credible report od fish dying or getting sick because their water was too clean. That does not mean pure, it just means free and anything "bad".
The only time I will change water more often is when I have an uncycled H. tank or need to remove something I had to add to the water temporarily (like salt or medication etc.). In an H. tank I will change water between daily and every 3 dayd at most based on the number a nd size o fthe fish and the tank size. The reason I do not use cycled filters in an H tank is some meds will just kill the bacteria as well as the problem. Also, I am not a fish doctor so I will not always get a diagnosis right or I may do so too late. If the fish is not cured it likely also means whatever the problem was it is still in the tank and filter media and any decor.
I almost never use anything I cannot bleach after I am done with the H. tank- curing the patient or not.