Southern Michigan is a very big area so it's very hard to respond covering even 1/8 of it. All along the west coast (the Lake Michigan side) there's hundreds of CG's and in most all areas close to a CG there you'll find places that rent boats and many having different sizes and motors. From 12' fishing boats to large pontoon boats or large runabouts with either outboards or I/O driven.
No need to go into Lake Michigan for big specie fishing if you don't want to as there are so many harbors, rivers, bayou's, lakes, and connecting navigable waterways with lots of fish to be caught. Bass, perch, walleye, catfish, bluegill, pike, just to name some. Boat launches are all of the state and here in the Grand Haven direct area alone (Northern Ottawa County) there's 39 boat launch ramps if renting a trailered boat that's not already in the water or will be put in for you at the rental place. Also 12 CGs here and they are building another big one presently. Yes, live bait also around here even at our Walmart and Meijer too.
Fishing and boating is huge in Michigan just like camping and RV'ing as there's over 11,000 inland lakes in the state and that does'n include almost 40,000 miles of rivers and streams or the Great Lakes themselves. Saturday, we ran our own boat over 70 miles and never even went into Lake Michigan. People in boats fishing or trolling for fish all over like always. Lots of bass tournaments here constantly.
Having your own boat is a lot cheaper than renting if you intend to go fishing a lot but that's your decision. A simple inexpensive used boat will hack it if you aren't going to go out a long ways from shore on Lake Michigan.
A superb CC LB 4X4, GM HD Diesel, airbags, Rancho's, lots more
Lance Legend TC 11' 4", loaded including 3400 PP generator and my deluxe 2' X 7' rear porch
29 ft Carriage Carri-lite 5'er - a specially built gem
A like new '07 Sunline Solaris 26' TT