Been to Duluth quitea few times. However, never in the summer time. I've been up in late spring when the boating season was just taking off. It is a lot shorter than the southern great lakes, but it's a lot more enjoyable (I've heard). I've pent a few summer weeks in northern Michigan (similar to Duluth). Summer days are only a few degrees cooler, and the humidity is typically a lot less. Lots of beautiful shore line up the Minnesota coast. A popular run is going along the shore to Two Harbors. Also, the Apostle Islands are only about an hour and a half tow away.
As far as the living situation, I'd seriously look at living in Wisconsin if you can. Superior itself is a dump compared to Duluth, but Duluth has an extra tax for just about everything you buy. If you don't mind a 20 mile commute, theres tons of open spaces in Wisc.
Good luck.
-Bayley