Conventional financing will use there matrix for front end DTI. Plan on around 30%, but they will go higher if you have little to no back end debt (ie credit card payments, auto payments, student loans).
They will allow you to finance properties based on your income up to that front end ratio. Remember this includes your primary home residence as well.
So for example, if you make $20,000 gross per month, they will allow you to have around $6,000 in PITI payments among any real estate you own. In the price range you are looking, that'll be around 3-4 houses. They will also require 80% LTV max, some will be 75%.
Your received income from rentals will not be counted towards your gross monthly income until you show at least 12 months of on time payments from your renters. After 12 months, they will let you count 75% of that as income. For example, you have a house that rents for $2000 for 1 year, you can now add $1500 to your monthly gross. That would bring you to $23,500 monthly gross income using our previous example. But because you can only have a 30% DTI, that extra $1500 only qualifies you for $450 in additional mortgage payments.
Hope that helps.
I am a licensed mortgage broker in Illinois and Indiana.