I would definitely talk to my priest about this. It’s hard sometimes for older adults to want to run here and run there and then be packed into a strange place. Explain that it’s not like a celebratory event like a graduation, where you have parents and others who are going to be with you and make a day of it. You have agoraphobia, you have arthritic knees, you have low blood sugar–I’d bring it all to bear and beg him for a private confirmation. I really doubt that you would be the first to request this.
I joined a couple of years ago, also a baptized candidate. I asked to join in Jan., and they slotted me into the RCIA program, which had been going on for several months. They were very nice about it. The group of us four went down to the Cathedral one Sunday afternoon, so the bishop could touch each of us and say hello. I hadn’t been eager for the trip, but with my sponsor and husband, it was bearable, and it was probably worth it, since that is the only time I’ll ever go there and the cathedral is beautiful. Our actual confirmation took place in our church on the Easter vigil. It was an impressive ceremony.
The more I read the OP’s post about going into downtown Detroit on a Saturday evening, I am seeing also that this may not be the safest thing to do, running around Detroit after dark. Another reason to bring up that agoraphobia. You should not be put through something that terrifies you, rational or not.
Definitely discuss this with your priest.