I don’t think you need to assign an email to the c&a account unless the reps do it in stealth mode as we’ve never had to give and from what I read online, it’s not required. I believe it’s tied to name and bday?
Yes it saves money. Also it may show sold out for your first day in the app but it’s listed for all days. No idea why they did it like that but will be active all days regardless when you select to buy.
Personally I wouldn’t start with MSC. From the west coast, there is no small 7 day Caribbean cruise, cruise where you want to. Don’t feel like you’re settling or you’ll already have preconceived notions.