Help Moving to Girona

We're from the United States, and we have two children who will soon be leaving for university.

We're in our late 40s and hope to retire in our early 50s to Girona (or somewhere nearby).

We are self-employed, and though we should have plenty of assets for retirement, we'd like to take the occasional job from U.S. employers. 

My Spanish is good enough for conversation, but I worry about being able to keep up legal and government language.

Is it possible to hire someone in Spain to help smooth the process for us (visas, taxes, residency if possible, health insurance, real estate deals, and general red tape).  If so, any recommendations?

You are so fortunate to be able to retire in Spain at early age. Yes, I believe lawyers in Spain will be glad to help you in any legal matters as they helped me a bunch. Good luck.