This statement specifically from the document requires an actual invoice, which means work has to be done or you doctor up a fake receipt:"Within 14 calendar days after completing the repairs or receiving the invoice or receipt, the landlord must mail or deliver to you a correct itemized statement, the invoices and receipts described above, and any refund to which you are entitled."

Be prepared for seller to stall, send outdated, inaccurate data and goose-chasing. my due diligence shortlist includes but not limited to- seller's Schedule E of 1040, copies of operating income statements for previous 2 years, rent roll, lease agreements, insurance binders, utility invoices, vendor service contracts, warranties, old inspections, survey.

Some people suggest sending an invoice if they don't pay.How were they late that many times and you did not notice.

Monthly I just download the transactions from the bank and assign each rent to the appropriate account.It doesn't seem worthwhile in my situation to create Invoices and go through the whole manual process of getting payments into Undeposited Accounts and then doing a Banking->Make Deposits payment.Is there a simpler way to use Invoicing or should I just stick to classifying the transactions from the bank statement?

If I don't get "paid", then of course they don't either.I was considering the "flat-fee" approach because I truly hate seeing all the nickel and dime charges for (paper, advertising, leases) etc..... however given the price difference between the (2), I think I can suck it up and look at each invoice knowing I'm still saving money.

FHA will generally require justification for the big price difference but I've gotten around that with showing scope of work and in some cases invoices for work.Regarding the inspection repairs, there are 2 inspections. 

Another tool that I'm looking for is a way to manage expenses & upload invoices in a cloud.

I invoice monthly, within a few days of the first of the month for the agreed upon % and any reimbursable expenses.Keep in mind AirBnB destroyed their Co Hosting feature by removing the ability to get paid through AirBnB. 

I include the legal wording as required by the FL statute regarding security deposit deductions, and include my contractor's invoice.

Again, you paid for a service you received.Lets say you bought a refrigerator at the local appliance store, were making payments on it and then they went out of business but still sent a invoice for the payment.