The answer to "do I need 5G" is no for the foreseeable future. Apart from the fact that you may not even have access to it where you live, 4G still have some some legs for at least a couple of years.
After that, will you "need" 5G: the answer is still no, in as much as even today when we are in a 3G-only situation we manage to do most things on the phone, so speed will only be a limiting factor for large data loads, like streaming (and even then, a small phone is not the ideal screen anyway).
In terms of memory, see how much you have and how much you've used. It will likely increase but if you use a cloud account for your photos and other large files you should be all right.