Congrats, sounds like a fun project.
Nitrates aren't really the enemy for most. Bacteria and dissolved organics become problematic much more quickly.
No to the 29, probably the 50.
No experience, hopefully someone else can chime in.
Yes. Check out the pellets sold by Al: https://www.aquaticsuppliers.com/
I fed my adults twice a day with no issues. Hopefully someone else can comment on fry.
Sponges are the cheapest but don't keep the bottom clean (becomes your job with a siphon).
Sumps offer a lot of flexibility but are easily the most expensive option.
HOB's are a good option if you want power filtration but don't want to invest in a sump.
Whatever option, water changes are still your best option to maintain water quality.
Depends on water pressure and height difference for the siphon. Bigger diameter hose (I think Python is 1/2" ID) also helps.
I use various PVC fittings and lengths connected to garden hoses. Hard to describe without a picture. You will probably have to age your water, so allow space for that.
If you don't enjoy water changes, it may be in your best interest to consider another fish. Just too easy to get burned out. At 26" tall, I bet your tank would look great with some angels.