I will give this a shot. I am on the $3 a month PAYG.
Q1: I know nothing about the Legacy plan. I understand it maybe better than the $3. Do you live close to a T-Mobile store? There shouldn't be any problem switching all your info to the nano SIM card. I had that done when I purchased an LG Stylo 3 Plus.
Q2: Call 611 (Support). Someone there should be able to answer any questions.
I just googled "Ultra mobile payGo SIM card kit". Try that. There is a bunch of sites!
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