First build suggestions

over 1000 dollars is more than enough money to build up a motorized bicycle. I spent 450 total on building up my first motorized bicycle, including a new bicycle, total engine kit, better wheels and sprocket adapter and sprocket.

have you looked at any kits from Staton-Inc? or GEBE?

I have a 2 stroke motor kit that was custom machined, and whilst very fast, it's no cruising machine.

I would recommend a bike with disc brakes as at the rear you can adapt your rear sprocket to the disc hub with a proprietary kit from the likes of Kings etc. I machined my own. You will probably have to change the offset of your caliper to suit as your disc will also be spaced out by the adaptor. Cable disc brakes 'generally' aren't as good as hydraulic disc brakes but having cables makes converting to a dual pull lever easy. The polo bike guys have some very nice 'expensive dual pull setups.

I would stick to well known big brands for your bike unless you're feeling brave. Most kits are to suit bikes with 26" wheels, though gearing for a 29er wouldn't be difficult. Just make sure you have enough space in your frame to fit a 4 stroke.

I converted my mountain bike to single speed so I didn't have cluttered handle bars. Some single speed bikes come with horizontal dropouts which may or may not be of benefit in terms of chain tensioning, and it may help if the bike has motorcycle style turn buckles to stop the axle skewing under power; assuming direct chain drive setup used.

Quality tires, tire liners and thick puncture proof tubes will go a long way to keeping you on track longer.

I would recommend the locally made components as a lot of the imported stuff is very low quality. I have fabricated my own fuel tank and am buying new needle roller throttles as the standard 'kit' stuff is rubbish.

The most important thing I can tell you is to look up and read your local laws first. I personally use Staton Inc. Always had good service and the kit so far has held up for over 4000 miles.

LRJ is right. Check your laws first. Search for posts about your state in the legal/legislation sub-forum on this site. Even if you don't plan to ride on the street, street legality increases the value of your motorbike.
Every member has their favorite motor. I would go 2 stroke with chain drive unless you plan to commute every day (4 strokes are better for daily commuting - no mixing gas and oil).
Friction drive is simple and efficient, but may limit your available riding days in the Michigan weather.
if you want a four stroke kit, use a beach cruiser. Four strokes don't always fit mountain bike frames.

LRJ,
Excellent point about legality.

I had to adapt a lot of parts to make them work in my HT kit, so factor in some basic things like it maybe necessary to have a round file to open up a sprocket to suit your hub and spoke layout, to having a drill to put a hole is the handle bars for the anti rotation pin on the twist throttle, wire crimpers to shorten and crimp terminals etc etc...

Some kits like the friction drive setups will save you some of those hassles as they are quite straight forward to fit