I have many friends who run / own many of the best bars and restaurants in Fells Point, Little Italy and Harbor East if you want recommendations based on your tastes.
Hmmm, never used the Charm City Circulator before, but I'd defer to Houston or anyone else who has on its reliability.
What you didn't state was how long you will visit and what interests you have outside of football and bars. We tell visitors to plan at least two solid days for Baltimore proper, or a week for all Maryland (mountains to Ocean City), or 10 days if DC is included. We recently had a good discussion with a Packers fan who plans to visit for the Ravens Packers game -- look it up for a lot of good info.
One suggestion by which you may appreciate the differences in how we each were brought up: go the the Fort McHenry Visitor Center to hear our slanted perspective of "winning" the war of 1812 against the Canadians and Limeys. Subsequently, go to the visitor's center at Ft York to hear about the American invasion of Ontario from a totally opposite slant.
btw: as to your running into other Ravens fans from Ontario: about a dozen years ago, we were at a pub in downtown Ottawa, running into some locals who professed to be Ravens fans; of course, this was a year or two post SB 35, when bandwagoners were fairly prevalent. Also, at the Ravens - Bills game about 6 years or so ago, we were literally surrounded by Canucks at the Orchard Park tailgating area. Obviously most were Bills fans (y'all make up a purported 1/3rd of the Bills' fan base); however, standing by the car next to ours were Ravens fans from Ontario
I stayed at the Hampton Inn and Suites just off the harbour when I came over in 2011, which was a great location as you're pretty much in the middle between Fells and Fed Hill. It wasn't too expensive either.
I can also vouch for the Charm City Circulator- it was great for someone who doesn't know the city and is free to use.