Personally, if Costco offers you the same special "Cover Book" I suggest you to buy the 128gigs tablet if you want to enjoy it for a long time.
I have a Galaxy Tab S4 and I already have 45 gigs used only for applications running with DEX and my normal applications in my internal stockage , everything then I can save is on my SD card (download, pictures, documents etc ) and those things take around 35 gigs space... ( I work a lot on the tablet)
If you buy it for games or for real multimedia using you'll need a lot of space... Fornite and other good games take about 2-3 gigs each and do not install on the SD card.
The screen of the S5e seems to be the same as the Galaxy Tab S4 and is simply beautiful. I prefer to watch movies on my tablet because it's better than on my HD-TV ...
This is my opinion