With the new firmware update that will probably be launched this month, you will be able to use any external HDD to store applications and games - something you have not been able to do before. It is easy to upgrade the internal HDD, but copying data over takes a long time, plus you are limited to a 2.5" HDD. With this new update, you could use any external HDD up to 8TB in size (and since these usually use 3.5" HDD, then you get more storage for your money).
So the size of the internal drive is less of an issue that it used to be. I just bought a PS4 Pro with the 1TB drive (I had added a 2TB drive to my previous PS4) so now I am just going to get a 3 or 4 TB external drive and transfer games to that.
BTW a typical game will be 30 - 50 GB in size - and even if you buy the game on disc, it will still need to be installed to the HDD.