I’m sorry that you’re in so much pain still, but good news Dr Osborne might be able to help you… Like @Isaiah_40_31 says, the back pain may well be from being tense & holding yourself awkwardly because of pain, so maybe not mention it at the moment to the neuro, focus on the ES/ neck related issues?
Food wise, I would eat as healthily as you can, avoid processed foods & too much sugar as these can make inflammation worse. If you’re finding chewing or swallowing hard then smoothies with protein powder or protein shakes might be a good idea?
Try heat or ice if you haven’t already, & there are medications which can help, there’s info here if you haven’t already seen it:
ES Information- Treatment: Pain Relief, Medications and Alternative Therapies - Welcome / Newbies Guide to Eagle Syndrome - Living with Eagle
I hope that your appointment goes well tomorrow, and if you can get surgery with Dr Osborne then it might be an idea to start a separate discussion to ask about info around the area when you travel there?