I am reasonably new to BBQ'ing myself having started doing so only a little less than 2 years ago. One of the things that confused me at first was when I would ask a question and get a whole range of answers about things, like time & temperature. One of the reasons for that variation, I have now learned from my limited experience, is that there are many different paths that can lead to great BBQ, and ultimately there is no one right answer. What matters most is the meat being done when it is done. You asked if 250 is a good temperature to cook ribs at. Of course it is. So is 225. So is 275. It is probably okay to cook them even hotter too. Is it better to wrap or not? Yes. Both work.
To answer your questions tho, more specifically (again, based on my limited 2 year experience), 250 is the temp I usually shoot for when cooking spare ribs (or brisket, or pork butt, for that matter), but I don't sweat it if it is a little higher or lower. Around 5 hours or so seems to be a good estimate for when spares will be done at that temp. I use the bend test to determine if they are done. I generally rest ribs about 30 minutes (but, again, some will rest longer and some shorter).
At the end of the day, what really matters is how the ribs turn out for your palate and that of the people you will be serving.
22" OTG; 22" Performer; mini-WSM; Brinkmann gasser; UDS (on the way); Maverick ET-732