There is not a single answer. In our experience with about 180 gb of downloaded maps, our Android tablet frequently choked and required downloading all over again. However, that was with micro sd card storage not resident storage.
We looked into the issue and hypothesized that resident memory might not have the problem and we looked at the various differences between Gaia Android and Gaia Apple tablet. We decided to bite the bullet and shift to an IPad Pro with 1 TB of memory (not just for Gaia - we do video and photo editing as well). The difference is night and day. Maps download faster, nothing has choked yet (around 250 gb of downloaded maps) and we like the Gaia interface better on the IPad. Believe me it hurts to say that - I've scoffing at Ipads for many, many years!
The degree to which you can zoom in depends on the resolution that you choose at download. More resolution, more zooming but longer downloads and much greater requirement for storage space. Some of the maps are in vector format on the Apple platform which greatly decreases the space and download times. I think Gaia plans to move to vector in the Android side also, but we didn't want to wait.
Howard Snell