My property manager recommended 4x mowing in the summer (not sure if that's excessive) which comes out to $120/mo

And also what % you guys feel is tipping into excess where it will possibly inhibit other long-term investing goals of buying other properties, etc.  

He traded property that he was tired of managing that he paid 20k for that is loosing value plus 100k in cash.

In the meantime, it’s 8% preferred return (cumulative) and 75/25 split (75 to investors) on any excess rental income.

What is the best way to go about raising the rate to create more cash flow without loosing tenants?

Do you guys think that I am being too conservative or are others just being too loose with their money?

You are likely to end up with a bit of turmoil with that cheap of a property (probably not in great shape and/or in a bad neighborhood) and lower-quality tenants (evictions, excess repairs, etc.).

I'd love to get an audit of the actual charges for the last 3+ years and see if there was any excessive overcharges or such.

In a small number of those cases you may loose a bit of money evicting someone that would have otherwise paid most of the rent but it will pencil out to a higher profit margin over the long term.

We did not loose much money but it sold for a lot less than some of the property tax valuations and the RE took a lot or time (overseeing the repairs from 2 hurricanes).I still love the location of the property and may go back there to vacation but as an RE investment it did not work for us.