It's a block-by-block play that in my opinion & requires a visit so you can determine where you feel comfortable and also to ensure that you situate yourself where shopping (grocery shopping) is closely available. 

To obtain impact worthy return requires a lot of units.  

Property Requirements: Are there any specific requirements for the property being purchased, such as condition, location, or type?

What are typical down payment requirements?

You can househack with FHA or conventional financing - FHA will require 3.5% down and conventional requires 5% down.

I am starting to build out a site to help with an agent's lead collection and online brand.

While this may exempt it from being classified as a rental activity, active participation remains a requirement, necessitating compliance with three tests: spending 500 hours on the property, dedicating at least 100 hours (and more than any other participant), and performing all the necessary work needed.Additionally, long-term viability and consideration of depreciation recapture are important concerns.

HELOCS do exist for rental properties but you are usually capped at 65-70ltv and these will most likely require a full underwrite that takes into consideration taxes, income, dti and all the normal quasi-associated red tape.

I've also had one potential tenant tell me that "an income requirement of 3x the monthly rent basically disqualifies single-income families".

Many thanks for your reply Jonathan, yeah i see lots of STR online, just wanna be sure about regulations.