I’ve been fishing Osakis for over twenty-five years, although only once in September, so my advice for that particular time of year is limited. Osakis has a LOT of Northern that are usually easy to catch pretty much anywhere, although their overall size leaves something to be desired. It is also a very good walleye lake: during the summer months crankbaits and jigs have their moments, but live bait fished on slip-bobber rigs or trolled is the way to go most of the time for ‘eyes. The lake has a lot of structure, so for walleye look on the deep weed edges (about 18’) off those bars and reefs.
As a family we stay for a week at Idlewilde, which is on the edge of town, and a very nice resort. I have camped over weekends at Linwood, which is also on the south end of the lake near town, and they are a good place as well.