@Robin Brown it depends on a number of factors.

What are other DTI factors should I look out when purchasing to satisfy lenders approval?

From there, you'll find that based on these factors, your tenant base will find you when you list your rental as available.

The house I purchased was recently renovated so rehab wasn’t a factor in this deal, but being a STR I wanted to go with higher quality furnishings that would stand up to more abuse. (2 years in and that has paid off so far) But I went about 20% over my estimated budget.

Although mental instability may be a factor in this equation, trying to build mutual respect and understanding is a good place to start.

But I'm just trying to figure out how different factors play into each other and how to come up with common metrics, and learning what to look for to determine what a "good deal" means to me.

CAP rate vs ROI : https://www.stessa.com/blog/ca...This site uses 50% rule for operating expenses, I've also seen 30-35% used - use your own judgement when calculating, depends on several factors like age of property, type of tenants, weather/location, etc.

While the interest rate on the loan is important, it shouldn't be the that factor that breaks your investment. 

I’m sure there are many other factors in answering this question. 

Can I eliminate Cap Ex for a while and just factor in repairs & maintenance and vacancy?