Lenses are more important than the body - they collect the light. Lenses also last longer than bodies - much longer. I have a 50 year old lens that I use. Lenses tend to hold their value, as bodies depreciate pretty quickly.
As to when to upgrade - your checkbook, your timeline. Then the question of what lenses, is actually the most difficult. What do you want to shoot? - land and city 'scapes, portraits, concerts, architecture, street, everything? - using wide, normal, and/or telephoto? Type of lens, manual, AF, zoom or prime?
Price is the great discriminator. Given enough dollar$, you can acquire just about anything you can find. It$ a combination of what you want, coming acro$$ it and then being able to afford it.
Personally, I would start to make a list of what your desires are and list a lens type with it. As you find out more, refine the lens selection, while you are hunting. It is particular galling to see one lens, while you are looking for another, only to find out later that now you are interested in that particular focal length. The point is run some parallel searches across items, rather than a very specific serial acquisition approach.