Expired SEP rating and starting ATPL

[Jaair]

I'll be starting the ATPL theory (distance learning while working full time) this summer and was looking for some advice on my current situation.

I currently hold a PPL with a SEP rating expired since summer 2017 (I have approx. 45 hours logged).

Considering the fact that my flying skills will be quite rusty, would it be more beneficial to get the ATPL out of the way first? So once the ATPL is out of the way (approx. summer 2019), I'd revalidate my SEP rating and get my flying skills "up to speed" during hour building before commencing the CPL.

Secondly, if this route were to be taken, would I need to get my CPL within a specific amount of time after passing all of the ATPL exams?

Thanks