Debt Service Ratio

[Steven Gitter]

Hello all.  New to BiggerPockets. Currently, I own my primary residence and a rental condo.  My question:

My primary residence has a mortgage of $3400 and the value of my house is $850,000.  Total expenses for the year are $40,800 which is roughly 5% of the home value.

My condo costs $1080 a month (high HOA) and has a value of $100,000. Total expenses are $13,000 which is roughly 13% of the value. My condo pays for itself and if I rented out my primary it would cover itself as well.

Question: Is there any metric you use or ratio when looking at debt service or is it all about the numbers?  I'm sure, there is no one answer to this question but wanted to hear some opinions.  When looking for rental properties is there a specific % you want the debt to be in relation to the value of the property?

Thanks in advance!