Would it be a good idea to put in mobile homes (assuming that we could get approval from the township), put in storage spaces that could be rented out or to build additional rental/condo units? 

You can diversify within real estate itself, be it acting as a private lender, purchasing notes, investing in a fund, buying a storage facility, etc. 

Storage shed on property for maintenance.

And tell them you will dispose of it afterwards;  you are not a storage company. 

There is a 38-unit self storage facility listed on MLS with average rent of $60/unit; Built in 1998; located in Porter, TX, which is in Montgomery County (north of Houston).

I personally do it in the self storage sector and own multiple properties 800-1000 miles away. 

One great way to make a place look fresh is to replace all of the outlets, switches, and switch plates.

Storage shed on property for maintenance items.

If the tenant is excellent, then you may consider a slight reduction just to encourage them to stay but I wouldn't recommend more than a 10% reduction or maybe an improvement to the property like a new appliance, fresh paint, etc.

Please note that there is plenty of opportunity out there and if you try to do it all, you may very well end up scattered & eventually burned out.There's an awesome book/philosophy out there called Essentialism: The disciplined pursuit of less (versus the undisciplined pursuit of more) by Greg McKeown.I personally only invest in Self Storage.