When buying land, what should I add to contract to protect myself

[Eric S.]

I am buying triplex and separate parcel lot that is next to it all from the same owner. The empty parcel lot is next to the house. I am thinking of either selling the lot as is or eventually like to build on it and sell the house or possibly rent it out. Currently is just being used as extra parking for the 3 unit building next to it. I have never bought a blank lot before and I know there is a lot of language that can be added to standard Ohio contract to ensure just not buying useless piece of land such as it is zoned correctly, soil is good, able to get parking variances etc. I am putting in offer quickly and using the inspection period of the house to do my due diligence. 

What things would you absolutely recommend I have in the contract?

What things are good to have in the contract?

Also any other useful information to know about buying land or parcels without buildings. 

Even if I do not get this deal I would like to learn and educate myself more on buying land and things to look and look out for. Thanks and Cheers!