Hello, I am interested in buying a small single family house in a decent neighborhood (average median house price around 450k), but the seller would want to sell the land (50x100) next to it together for an extra 100k to make a deal. hypothetically I can negotiate it a lower price for the land (any suggestion on how to determine the value for the land), what kind of investment can I make to turn the land into something profitable rather than just being wasted?

set up your rentals on a weekly schedule.52 weeks in a year your picking up an extra month.. now lower your tenants rent by 10 bucks or 190 a week.and your tenant is thinking hey is am saving money when in fact your making money.rentals in AU are collected weekly and advertised weekly.  

Location also determines the demographics of your tenants.

My last real estate transaction the attorney showed up at the closing to pick up his check, I don't recall him doing anything meaningful with the transaction at all.

I can’t say I know anything about how things are done in Michigan, but I would think a ‘Certificate of Occupancy’ is different than a ‘Rental Certificate’ A CO is an inspection and determination that a space is habitable.

And very least,  it will tell you the steps  to take so that by the time you finish the course ,  you've already applied or understand how to apply to dbpr for the state license  and  how to determine  where you will be testing. 

Also, keep in mind that the tenant would pick up some of those other bills (water / sewer / trash / electric / heat). 

From what I can tell, the land tracts that were picked in most states aren't exactly "war zones"

We wanted to rent it out on the lower end of the rental market to have constant renters and then the pick of who we would want to rent to. 

So you determined that it would be more beneficial for you to retire the title.