Hi, Ben! I thought this would be a fun post to put together, so here goes. In the heart of Minneapolis, there is a Chain of Lakes consisting of Lake of the Isles, where Mary Tyler Moore's TV house can be found, Lake Calhoun and Lake Harriet. Here's how they are laid out:
Lake Harriet is a very popular destination with a bike path and separate pedestrian path going all around it. There is always somebody walking, jogging, biking, rollerblading around Lake Harriet.

But, what makes Lake Harriet really cool is the historic band shell and refectory located at the top (north end) of the lake. See those castle-like buildings in the photo below?
On summer weekends and evenings, there is always something happening there, concerts, boating, trolley rides and just general merriment.

To the right of the band shell, is the refectory as seen below. There is a little snack bar in the refectory which serves delicious ice-cream, the best popcorn, cool drinks, etc. Plus, it has restrooms.

Lake Harriet has hosted many 5ks in the past. For these really big events, they close off the street that also circles the lake and that is a sanctioned 3.1 miles.
Here is a more detailed map of another 5k here.
The pedestrian path around the lake is just 2.75 miles, perhaps we could take a little jog into the charming residential area that surrounds the lake to make it 3.1 miles.
Here are some other links to past Lake Harriet 5k events:
The Reindeer Run
Red Cross Run for Blood
Hey, I just found out that there is a Valentine's Day 5k coming up on February 12th. I should go and check it. Eek! My first 5k! BRB....

Oh, man. I did it! I signed us up! My husband and I have been running on the treadmill for months, time to take it outside! Gosh, I hope it is warmer than today (-3 degrees F., that's -19.4 degrees for you, E. <3)
Here's a cool link for a running group that set up an outing for the 100% Irish for a Day 5k last year, just to give you some more ideas. It would be kind of cool to set up pages like that for each city on your tour. Might give you a good way to judge potential turnout, brainstorm even better ideas for each location, etc.
Now, I also want to tell you that the next lake up in the chain, is Lake Calhoun shown in the photo below. It is also a very hip, cool place to run with a cool view of the Minneapolis skyline. The pedestrian path around that lake is exactly 3.1 miles.

I only mentioned Lake Harriet first because of the how cool the band shell would be for the beforehand venue. There are big picnic areas on Lake Calhoun which could work as a gathering place, no stage though.
Here is a link to an information page about the Lake Harriet park.
The phone number for reserving the bandshell is 612-313-7796. Like I said, it is really busy on weekends and evenings, but I have never seen an event on a weekday morning in the bandshell, so I bet availability wouldn't be a problem during the week.
Oh, and as far as an after-run venue, as I mentioned, there is a Whole Foods nearby. I haven't thought too much about that though, but since it is a very popular area, I'm sure there would be many food options.
So, Ben, that's my idea. Just a thought. No matter where you end up having it, we'll be there. Can't wait!
Best wishes for the tour!!