If it's not an ironclad legal ROW, you are taking a significant risk. 

When existing tenants are on month to month rental agreements then you can proceed with legal notice of intended changes.

Even the lowest priced house still needs to offer any future resident safety and this area can lead to various very undesirable legal liabilities for the owner/seller.

If you are doing these for legal reasons, quote three sources.

I don't think ethically legally they can "price you out". 

If there is any legal existing easement or right of way they will have it on file and be able to show it to you on a map.

If you're going to finance the deal, send a pre-approval letter or something similar along with your offer.

I think I should be going through the pre-approval process within the next week or so in order to have a better idea as to what my financing situation'll potentially look like.

Check with your local laws but simply give them proper, legal, notice that as of "xx" date, their new rental rate will be $xxx.

I’ll let someone familiar with New Jersey law answer your question about online only rent payments (it wouldn’t be legal in my state), but I did want to caution you against accepting a check as payment for the initial deposit.