Based on what is said above and what I've seen, there are some things that can increase your viewcount on completed works:
1) adding bonus content (preferably to the work itself so subs have a reason to stick around after completion)
2) publishing new stories on the same account which will draw people to your older work (preferably with only a small gap between releases)
3) promoting on social media, other platforms, tapas events, etc.
As for your second question, I;ve seen both done on tapas, but because subs or likes dont drop of if you keep the story in one long series it tends to be more favourable to keep every part of your story in one long series (even if it may scare away some viewers if its really long.) Some people use different 'volumes' to demarcate different parts of the series.