Their functionality is similar, and any of them will do, as long as your client uses them consistently.And this is where the weak spot really is: how your client uses it.

In my minds eye it could allow for collective resources to compete with the functionality and easy user interface of Zillow.

This is a severely distressed non functioning property and unless you are an experienced MF operator or bring one on board, I would be very careful.

Other IMS not mentioned above are: Update Captial (https://www.updatecapital.com/)Invest Next (https://www.investnext.com/)AppFolioI have done a demo with most of the software, and I like IDR the best from a cost and functionality perspective.

It's not needed at this level of operation, and a Cozy.co or a Hemlane  would work much better for your scale and function, while keeping it much simpler. 

It’s designed this way and functions like you want and as @Patrick McCabe described.

Having one based in CA, or at least familiar with California laws, would also be a good idea as CA taxes tend to be more robust than most other states and if you're a CA resident, ALL your income will be taxed for CA purposes. 

That is the primary function of CAP RATE: to do a high level comparison of investment types. 

I realized that as a newbie investor, I could not compete with investors with robust systems in place.

K&T is par for the course around here and as long as it is functioning normally then you just need to make sure that you do not have 3 pronged outlets being used for ungrounded lines.