You can do probably 60-70% of the game just with base version. You won't be hamstrung by missing meta sets or content. Even then, DLC sets that can be crafted can still be obtained by having someone else craft the for you, or by having access to tables via a guildmate (like 95% sure it works that way, if not, you just need the 3rd party crafter). You'll obviously miss the new zones, dungeons, trials, and skill lines, but you'll still get over a hundred of hours of content.
You can absolutely play this casually. The base game stuff is pretty easy in comparison to how it was, with power creep and such, but it's, at worst, a good, long introduction to the game systems to better gauge your future interest.