How to get into the second arc of an ongoing campaign and where to go next afterwards

[L8er]

Hey everyone, new to the sight!

I'm a relatively new DM, I've ran a few campaigns here and there for context.

For my first question:

My current group that's on and off in consistency are going to finally finish the lost mines of phandelver! Also they will be level 5 by the time it has ended.

I'm going to give some down time to their characters after and was thinking of somewhat segwaying them into curse of strahd through one of the characters that has been having these visions and being beckoned by strahd (without his knowing, I've made it all in his mind and we've kept it between ourselves as far as I know his visions).

I was thinking something like once they came back, the character in question sent them mail (that was actually strahd) while being ominous about fog that's lately been appearing all over never winter, then bam they enter but any help would be welcome here.

For my second question:

Black Friday is coming up so I'm looking to get another module or sourcebooks to enter the third arc (if they survive...) Or a possible new set of adventures to give their current characters a rest.

Any ideas?

Thank you for any and all help! Glad to be part of the community :)