@Scott Sambrook conventional (Fannie/Freddie) underwriting standards only require 6 months' seasoning before a new appraisal can be used to determine the value of a property for refinance purposes, but in my experience most lenders still want to see 12 months of ownership before they'll play along with that.

The interest will need to be traced to accurately determine tax treatment. 

What is the best way to determine a reasonable rent expectation?

The GRM varies by area, but this should help the appraiser determine value.

Inexperienced investors tend to (1) get exited about deals without having the experience, knowledge or ability to properly determine if indeed the deal is good, bad or mediocre, (2) take what the seller says as gospel not realizing most sellers will exaggerate, lie and or withhold vital information to get what they want, (3) engage people who will provide opinions for free rather than pay a competent professional, (4) get emotionally caught up in the deal and very defensive when receiving an opinion or information that doesn’t support their dream, and rationalize that more experienced people who point out flaws are “jealous, negative or haters”.Btw, no one can provide any knowledgeable answers to your questions without first analyzing the deal, your ability to come up with a down payment, your credit capacity and banking relations, if you have a track record, your experience with similar property ownership, etc.

There is not much you can determine from just economics, we recommend strong personal guarantees from the principals who will be the beneficiaries of your purchase.

You should be able to build it out for about $250k and you then just need to calculate how much monthly/yearly rent you will get to determine how long it will take to recoup your investment. 

Determine how long you will likely own the house and costs (taxes, utilities, etc).  

I'm just curious how some of you experienced property owners determine how much liquid money to keep on hand for a given property, if there are important reasons to keep that money in a separate or LLC bank account, etc.

Have yet to determine which strategy(s) will best achieve our goals.