They simply charge a flat fee per transaction and no monthly dues.

If each investor is doing a different deal, then your options are to create a new LLC for each deal with your LLC as one of the members (great idea) or simply have your LLC put together a joint venture agreement with the investment partner.

There are lots of resources out there, a great one is simply to go find your local for-rent advertising sites that will publish what other housing is currently being offered and for what price.

Yes, naturally, financing a renovation will lower your equity, simply because the mortgage balance is higher, relative to paying cash for those same renovations. 

This is a much different set of laws and generally more restrictive and much costlier than simply borrowing.

If it was in the details and you simply did not read your lease before signing, call it a lesson learned.

Generally, I wouldn't care as I would think there would be minimal damage as it relates to this install and would never had questioned if they simply installed the cameras without asking to begin with.

I've considered simply buying properties with that cash and avoiding financing all together, but I'm afraid that will lead to a significant portion of my cash "sitting on the sidelines" more often than it's being put to use.  

So you could simply set up an S-Corp and transfer the LLC to that. 

When you go to sell, if the item is still showing on title, you'll simply provide your owners policy to the title company / title insurer involved in the sale... who will obtain an indemnity from your title insurer and/or from the insurer who insured over the item in the past.