HI.....Lots of things vary by region. Allergies are almost a fact of life everywhere today and sadly, we've done it to ourselves. Generally they kick in about 2 yrs. after you've moved.
There are some great answers to your question, but homesickness is probably going to be your biggest foe. It seems that no one is ever quite prepared for it.
Insofar as medical care is concerned, this can vary from state to state. Your company may offer a wonderful plan, or one that isn't so great.
People like Dr. Nancy Klimas (I haven't been to her) out of FL are excellent, and many places such as The Cleveland Clinic have excellent departments. It's very hard to get answers to all of our problems, but then you already probably noticed that where you are.
One of the first things you should do is find a neurologist or rheumatologist who will specialize in the care you need. A fairly modern facility is best b/c you'll have access to newer MRI's and other machines that may be needed. I tell people to keep all of the documents (copies) and they're easily available at a dept. next to where the MRI (for example) is given. Keep copies of all blood tests as medicine is literally changing by the day. You'll have a deductible each year with respect to your insurance.
I won't even mention Medicare b/c you don't look old enough for it. Medical care can be expensive, but it is quite thorough IF you get the right doctor. I'm not cured, don't expect to be, but my doctors do care and keep me as comfortable as possible. Dentistry and eye care are separate from medical insurance, so bear that in mind. Prescription costs can often be cheaper than insurance by the use of something called a Gold Card...ask your pharmacist about it. They're readily available.
You and you alone have to decide on where you want to live. North will definitely have a winter flavor, but in the south or places like TX (where I am) the hot weather can get wearisome from about mid-July on. If you're used to that....fine. The winters can be very mixed. There are a lot of places to choose from....rent don't buy to begin with. That way you can decide at your own leisure where you'd like to settle down. Good luck. Yours, Lenora.