April should be a good month to go as winter is holding on strong up here. Be careful wading as we have had our fair of snow here in the Detroit area and Newaygo will have 4-5 times that due to the lake effect. Flows should be fairly healthy by April, don't forget the felts as the MO is a fairly big river compared to some of our others. If you prefer floating line consider a bobber rig (bring your roll casting A game though if you go this way) but don't overlook a running line and chuck-n-duck (you can do this with a floater but you will have to watch the belly close).
As for flies, PM wigglers, black stones, and other common nymphs will work well. However, there should be plenty of fish in the system by that time (they are predicting a good run over there) so make sure you have a good selection of egg flies. Between the steel and suckers the river should be full of eggs.
Hope this helps.