@Zach Powell
@Brandon Sturgill gave you an important "heads up". Do not ignore it. I'm NOT an attorney but I understand Ohio Land Installment Contracts pretty well and I have over 30 years of experience with them as both a buyer and seller.
There is a gray area that you'll need an attorney to sort out because if it "hits the fan", the following may matter. Ohio law requires certain protective features for LIC's when the buyer is an owner occupant; i.e., when it is a consumer transaction. Many of those features are not required for business to business (non-owner occupant transactions). You've spoken in terms of a singular land contract which presumably was written based on the owner occupant standards for all 4 buildings which is a plus for you BUT you need an attorney for several reasons and the attorney can tell you if the document you have was done correctly.
As Mr. Sturgill has correctly suggested, you are now (very likely) at the mercy of the seller. The fact that you imply he is still accepting payments is helpful to your case but he can change that in 10 minutes by sending you a letter requiring you to pay the full amount (I don't recall the law on this point and it may be that since he's accepted payments he has to give you 60 or 90 or some other number of days to get the money but he can demand it).
The fact is that you've got significant liability. ALL THAT YOU'VE DONE IS AT RISK. You say he doesn't want them back? Maybe that's true but maybe he doesn't know what they are worth today. Or, maybe he has a heart attack and he dies tomorrow and his heirs have a totally different way of looking at the situation. At the risk of insulting you, you are a fool if you don't speak to an attorney who has a strong history with land contracts. If you want to be an investor, you have to be ethical, honest and fair but you also have to be protective of your interests. Oh, and by the way, you don't have the deed, only a promise that he will give it to you. From day one you should have had that placed in escrow pending full payment (you can arrange for an escrow now with your land contract's new terms) or, even better, change the deal to you getting the deed now and you giving him a note and mortgage. He's had years of you paying on time, he should be comfortable doing that. That way you avoid banks altogether. Even though you may be able to get a slightly better interest rate at a bank, by time you pay for the appraisals and costs you will almost certainly be in almost the same position financially and have a far more flexible mortgagee. There's lots of ways the note can be written that will be beneficial to you and to him (he can get modest periodic balloons if needs them as an inducement, for example).
Bottom line - you are standing with your pants down around your ankles. Whether you trip and fall and lose it all or stop, pull them up and get headed in the right direction is all up to you.