For tax purposes it would make bookkeeping more difficult but as long as you track and attribute the expenses to the correct properties you could do your tax return.You would however be risking the asset protection that the LLC is providing you.  

Works for marketing, mailing lists, bookkeeping, etc. etc. 

I'd hope to hire a CPA who also invests in real estate for tax planning and bookkeeping.

Assuming to keep book keeping simple......

I'm an accountant who has 800+ credit scores (according to MyFICO 3B monitoring) and an established small bookkeeping practice.

Contractors will go where ever there is work and the city favors tenants thats why good book keeping is essential.  

In the future I would probably move towards larger multi family buildings, that way you can tend to just one property rather than ten different ones and at the same time keep track of all the bookkeeping on each one, maintenance schedules, etc. 

I once sued an HOA President in small claims court (no luck with the cops because they said the HOA had too long a history of "casual" bookkeeping & monitoring practices).

I'm already working with some VA's for bookkeeping in buildium and quickbooks, data research and creating seller databases.  

It is true if you are taking care of bookkeeping currently, you can continue to do the same no matter where you are.