Welcome to the forum, so glad you found this place, it's great!
I have RA, so I don't know much about the psorasis type of arthritis, but there are several here who do, so I'm sure someone will come on with some advice for you.
As far as the gradual onset though, that certainly was the case with me, and alot of what you're saying sounds like what I went through, especially with the fingers and wrists. I could really relate to the driving thing! With RA, I have a flare which causes joint pain and swelling for up to a week or so, then it subsides, and the area can still stay tender for quite a while after.
When I was first diagnosed, I was in a bad flare that travled all around my body, that's what forced me into going to a rhuemy. I told her "this hit so fast" and she just sort of smiled and said, "no, this started at least 2 years ago". When we backtracked through my history, all the little things that I just sort of ignored as no big deal, were really the first signs of RA. It just finally progressed to a point where I couldn't ignore it any longer.
So, try to hang in there, it's so great that you have an appt this week! Let us know how it goes.
Just had a quick thought for you, it might not be a bad idea to write down your symptoms, just like you did in the original post. Include when you first noticed things, how long they lasted, pain levels, as much detail as you can. Think it could be a big help when you see the doc. I know I always walk out of the doctors office and on the drive home go, "oh shoot, forgot to ask about...." This might be a big help both for you and your doctor. I always write things down in the doctor's office too, there's only so much info this old brian can hold on to at one time, ya know. I need cliff notes!
Are you seeing a rhuematologist? If so, they should have a good feel for what's going on..If it is RA, the sooner you get treatment started the better.