The good thing I have seen doing work for active military families is if for some reason they don't pay (which they usually do) if you have your office/billing department send the invoice and copy of the job authorization form (contract for the work to be done) to their commanding officer once the invoice is I believe 30 days delinquent (for landscaping anyways) as long as the work has been completed the military will cut you a check and then somehow I guess they get payment from the soldier however they do that (I'd assume they just garnish their wages). 

Furthermore, please note in support the following reg refernces:I say this because effective for taxable years beginning on or after January 1, 2016, the Internal Revenue Service in Notice 2015-82 increased the de minimis safe harbor threshold from $500 to $2500 per invoice or item for taxpayers without applicable financial statements.

The management company takes the electrician bill, adds a "management fee", re-invoices the bill to the management company's invoice and sends that bill to the owner.

The service company who reads our Sub meters and invoices my tenants on my behalf?

Your GC's invoice should inclued lein releases, or "partial" lein releases from each sub he is paying.

So before a work order begins there will be an invoice that is signed.

So you don't have to mail out a bill (an Invoice physically) just shoot over an e-mail.  

If it was a lot of damage, I would invoice each job separately (drywall repair, door repair, door casing repair, etc.).

Keep receipts for parts/materials, invoices for hired services, and yes charge for your labor if your jurisdiction allows it.

I would be fine with dropping it off at a office, however for me I have tenants in two different towns and it's a 30m drive between them (meaning 1hr round trip) which can kind of make it difficult for a tenant to do.I'm still leaning towards sending monthly invoices showing them what the rent is, due date, ect so that what they pay/when they pay is put in front of them every single month.