I would just skip the stupid spa panel and buy a GFCI breaker. Its cheaper and you don't have a NEMA 3R box inside, Not like thats a big deal but less looks better. Its a 50A Main Lug Panel.
Q2: What are your goals?
Q3: GFCI Breaker
Q4: Yes you can take it with you.
Q5: Spa panels are stupid...