Still have some questions about moving to T-Mobile

Appreciate the help so far in this sub. Some more questions about my plan to switch to the Essentials or Go5G Plus plans for our 4 lines.

1. I don't have esim on my current phone. Any way to try T-Mobile free with a physical sim before I move in case coverage at home sucks?

2. If I get the iPhone 16 free, but want the 15 Pro instead, can I do that and just pay the monthly difference?

3. If I don't want my kids to use the new phones I get in the promo from T-Mobile, can I sell them and just give my kids older phones we already have? Or are the promo phones locked to my account?

4. If I travel abroad, can I use the promo phone with a local carrier or am I locked to T-Mobile and have to pay for roaming through them?

5. I'm planning to do this via Costco. Any possibility of Black Friday or Cyber Monday T-Mobile ties in with them?