Your post reminded me so much of my first 50+ ride after a 30+ year hiatus from cycling. There is little to add technically to what DLV advised you. That was a polite, thoughtful, informative post.
As you build up time and miles on the bike, keep chatting with the folks at the LBS, and other riders. You'll get dialed in eventually, either because of changes in your physiology or tweaks to the equipment advised by others.
As far as numbness goes; I find I read far fewer pages than I used to before the legs go numb during my morning library visits as well. I guess 50+ and 200+ are just large numbers which have certain characteristics for all of us.
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Just Peddlin' Around