Quite a few years ago I learned my lesson about buying a machine with limited amount of storage.  It was fine for a while until I kept adding more and more to my iTunes library and that really started to become problematic.  I had already put some folders and files on the external drives I had then, but did not want to put my iTunes library  anywhere than on my computer's internal drive.  Eventually I sold that machine and purchased one with 512 GB and have continued to do so ever since, and also once the Samsung T series of external SSDs became available, I began using them and that has made a difference as well. 
Given the choice between increasing RAM or increasing storage capacity, I would go with increasing the RAM, as the storage capacity can always and easily be supplemented by external drives, either SSD or HDD.