Does installing GApps save space compared to PlayStore install? I am about to clean-install a Lineage ROM on my Android and I want to maximize the internal storage space left for the apps I want.
What I understand so far is:


The GApps package will reside in  the /system read-only partition.
Updates of apps from the GApps package will reside in the user partition.
Apps installed via the Play Store will reside in the user partition.


I see the two following options:


Install a lean GApps package (e.g. OpenGApps pico) and then install the apps I want from Google's Play Store.
Install a GApps package which includes additional apps (e.g. OpenGApps mini).


Question 1: Is there a drawback to making the /system partition as full as possible by selecting the biggest fitting GApps package?

Question 2: If I need some Google apps such as Maps and YouTube, which option maximizes the space left available to install other apps, updates and user data?

Additional information:


The device is a Motorola G 2015 (osprey) with 8Gb internal storage.
When comparing the difference between the mini and pico packages, the only apps I need from the mini package not included in the pico package are Maps and Youtube, all the rest is useless to me.
I can get the most recent OpenGApps package and it's ok for me to disable the update of apps such as Maps and Youtube if it results in more available user data space. (My aim is to extend the lifetime of my device by avoiding the lack of internal memory.)
I saw this StackExchange answer, but it didn't answer my question well enough.
Question 1: Is there a drawback to making the /system partition as full as possible by selecting the biggest fitting GApps package?


Whether you install the smallest or largest version of GApps, /system partition will remain the same, unaffected in term of its size. The partition size is fixed for the device by the manufacturer (Yes, if you are rooted it is possible to re-size the partition but it is not recommended).


  Question 2: If I need some Google apps such as Maps and YouTube, which option maximizes the space left available to install other apps, updates and user data?


When you install GApps from the recovery, they will be installed as system apps under /system partition. Then when you start your device, their data will be under /data partition as any other apps. Subsequent update and usage may (will) increase their sizes on the /data partition while /system will be same. Making new version or updates part of /system partition will allow to recoup some space from the /data partition.

If you need Maps and Youtube, install GApps mini, then disable/uninstall apps that are not part of the pico or nano packages.