If I have lump-sum free cash, should I just apply it to my mortgage to recast so that my monthly goes lower?

I have lower-end property in a small town.

Can I charge them fees & rent for storage of their crap? 

.), and also need to consider the cost of vacancies or bad tenants.I also recommend you charge market rate, for yourself and the tenant.

The buyer can obtain a property with no mortgage qualifying and or a lower than current interest rate, or on terms not readily available otherwise.  

However, I definitely recommend pictures any time a guest left damage or extra cleaning that will result in additional charges.

Rules for contractors NEVER use your money to fund a customers project ( unless you hold first lien position and charge interest )If the money stops , the work stops .Put everything in writing .

There's no charge to me to get these funds except a yearly fee of 200.00. 

Your main concern should be whether these bedrooms and bathrooms on the lower level are legal and have the proper egress require for fire code and livability.

Now I agree the 4 will cash flow better than one will but I also look at it from risk of 4 properties will have higher maintenance costs and lower priced properties tend not to appreciate as well as a higher value assetI am also in it for long game and managing one is easier than 4