too many questions for me but-
I have used in Canada, Europe and New Zealand on my phone. No issues. When I go over the 5GB get a notice but really did not seem slower for what I was doing.You do not do anything except set phone to Intl Roaming and Data (if you want).

Phone calls no issue at 25 cents a minute but rarely used.

I get the Netflix credit and when switched Netflix plans from the 1 to 4 no issues as shown on phone bill.
T-MOBILE SUBSCRIPTION
Account Netflix Premium (4-Screens) - T-Mobile Offer
Includes $12.99 Netflix Discount
$7.00

Texting is a free benefit. Never billed for texts.

I have been on Magenta Max 55+ for almost 3 years (moved from California on ATT). Never looked back. 5G service in LAS and no issues with coverage. Never a billing question. Just switched my Internet from Cox to T-Mobile a few weeks ago.