Put the maps on an SD card.
I don't think that would work, I think the supplied Topo map is keyed to the device.
Your images were a bit indistinct so I plugged a 30x into my PC and got a report of 216Mb free space. (In my case I have added a UK contours overlay map which occupies about 100Mb. Other added maps are all on the mSD card.) If you add planned tracks and routes for a long holiday, these are unlikely to take up more than 2Mb (and I have found that it is better to store these on the GPS, not on the card).
Daily tracklogs are archived on the device but they almost never exceed 500Kb per file, and often much less. So in practice (with over 200Mb of free space) there is space for over a years-worth of daily ridden archived tracklogs. And of course you would copy these elsewhere at intervals, and so keep the GPS storage under control.
In short, I would say, nothing to worry about. X-post.