I grew up on Portage Lakes and still fish them nearly every week. There are tons of decent crappie. I like Rex Lake, especially the south shore wherever I can find submerged wood, weed edges, or docks. Minnows fished under a bobber will take a lot of fish when you can find them schooled. Spring is best, but fall is good.
There are fair numbers of yellow perch. I often find them schooled in deeper sections of Turkeyfoot and Rex Lakes. Use a fishfinder if you have one. Minnows or nightcrawlers fished on crappie rigs or spreaders Lake Erie style will catch them. There are not a lot of jumbos, but you can find some decent sized ones. Places I've caught perch in good numbers before: Turkeyfoot speed lanes, Turkeyfoot in the main channel off the State Park beach, deep side of the island as you enter Rex Lake, Rex Lake off the old Masonic Park, and Rex Lake in the mouth of the rectangular bay on the south side of the lake. You'll occasionally catch them fishing for crappie sometimes, too.