does reducing pic size reduce quality?

[Mike1942f]

Yes, it reduces quality, how much depending on how you do it, so you always keep an original that is the max size you want to keep but the pictures you are uploading now are way too big and unless you really want people to enlarge and scroll them (where they can) there is no point.
For example, your 4200 even if put across a 2048 screen would be twice too big and cutting it to that size would reduce the storage size to about 1/5th the current, if not lower.
Take a look at some of the images on Facebook (I am not there) and right click and look at image properties (or image info) for the size - you don't really need to upload anything bigger.