Do we leave that excess in the account after paying the mortgage?

It appears to me that you are being excessively conservative in your time periods per capital expense. 

You can make it clear to the tenants that they will be held responsible for excess damage or waste caused by the animal,  just as if they themselves did it.While you need to be careful to avoid a claim of retailation,   maybe schedule the next couple rent increases to be a couple percent more than you otherwise would,  and bank those funds towards expected greater turnover costs.  

There are numerous part time agents in this area doing in excess of $3 million annual volume.I know this comes down to my own goals and risk tolerance, but do any of you have an opinion or advice when deciding who to go with?

So my buy and hold portfolio does spill off a fair amount of excess cash reserves .

The other avenue is going to be either even more fuel tax or a per-mile driven tax.   

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

I've become obsessed with the idea of using real estate to achieve financial freedom and to fuel my adventure travel lifestyle. 

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.  

If you have your tenants paying heat you should mandate it be with your vendor of choice so the same tank can remain in place.The fuel provider will also very likely run a credit check on the tenant so be prepared for that.