I tend to agree on the DIY to a large extent (delegating only where it is more efficient) but no one has more at stake in the deal than you, so steering the ship can be a great way to add value and avoid agency costs....can't wait to hear more of your ideas .

Using terms such as buyer and seller in an option will take down the road of an installment agreement determination quickly, options don't have buyers and sellers, the grantor is the optionor and the grantee is the optionee. 

I am handy (plumbing, electrical, general DIY) but will have to sub out anything major since I am full time in a tech consulting job. 

Space savings, does not have to run as much to keep water hot while not in use, so there is some gas / electric savings and they tend to last a little longer than hot water heaters. they are a little more in cost to install. i do not have any in my rental properties but have one in my personal home and i like them. make sure it is sized for the amount of bathrooms and kitchen it is feeding. mine feeds 3 bathrooms and a kitchen and does just fine - brand is Takagi. 

I have installed cabinets, cleaned houses, yards, ect. for there is not much I can not do in repairing a house.

Seller will pay all real estate taxes and all general, special, respread and reassessed assessments through the last installment immediately preceding the Closing.

Read All Of This Please Entering a contract with a financing arrangement turns your unilateral sale contract into one with bilateral agreements, you can not assign a bilateral agreement without the consent of the seller.A subject-to sale is an installment sale by the seller, you make payments and when the debt is paid off,  you clear the encumbrance with full title, the seller can't convey full title until the debt is paid. 

One possible solution, if it's an ancillary bathroom is to remove what's there and install a one-piece surround with tub.

So instead of asking what the condition of the roof is, I ask when was the roof installed or last replaced.

Florida homes are built on a slab so to install proper ac/heating you have to cut channels or venting channels in the concrete/floor you could come through the attic but that's not green and a professional would advise against it, is the ac your biggest desire to update?