This is personal preference - in theory you don't need to reinstall GApps but more than once I've been burned by "something" within Lineage removing the addon.d script that replaces AOSP apps with GApps.
The end result is that I ended up with 2 Calendars, 2 Clocks, 2 of some other apps, and terrible battery life/heat issues.
So personally, I *always* back up just in case, and always have a GApps zip on my phone so that if it happens again I can roll back the backup then reinstall the update *and* GApps.
Thank CloudFlare for their CDN network - I only have ~17Mb/s upload but once the first person has downloaded the image it's served entirely from CloudFlare