Is it just time and experience, knowing what costs what or is there a better way? 

You can save cost on a property manager by managing it yourself. 

You can then estimate the potential rents using Biggerpockets rental estimator.If you are willing to buy a SFH and rent of the rooms while you live in one of the rooms.

It cost more digital locks (camelot from Schlage), but the flexibility for travelers on FF and also AirBNB will be notable in a higher booking rate :)

Also study up on lease renewal restrictions and eviction costs in CA and LA or wherever you are buying. 

Yes there is risk on the Reno costs.

Then if you end up doing a self directed IRA instead of a Solo 401k from not having any self employment income, you are subject to UBIT rules, which can cost you thousands in fee annually just for the filing depending on the complexity - in addition to the tax owed. 

Having a person answer the phone costs the PM company substantially more than operating a support button with a delayed response.

That's where you wanna be project cost wise. 

All in after closing/holding costs we were all in at about $1,270,000.