Throwing in my two cents, from a relative beginner.

Shoot with what you have now and figure out what you are missing. given you impending trip to Europe perhaps there is an argument for a Zoom lens. You are beginning down a long road with many paths, and at this point it is hard to say which path you will take and therefore the equipment you need. Get some time behind the glass, maybe take an online course that encourages you to go out and shot, shot, and shot. Then you will see quickly what areas you need to focus for a lens. I would not worry about the Fx vs DX part at this moment, many things (as others have eluded to) will change between now and 3 years.

I would recommend a good tripod as your first investment, this will work regardless of Fx vs DX and will be with you throughout your time in Photography. I am so glad that I purchased mine as one of the first items after my D5300.

Just my thoughts, hope it helps. Good Luck.