I am looking to acquire my first property soon but wanted some ideas on how to proceed if the goal is to build the portfolio with buy and hold for the long term.

There are lots of quantitative metrics ("mainstream" as you say) to observe here (P/E for the S&P - see chart below, margin levels, ratio of total market cap to GDP, etc), & anyone with access to google can see the same numbers.

@Chris Heeren, I understand and agree with not wanting to be leveraged 100% of the ARV; I actually had a conversation with my wife after we got close to the closing date, realizing that we actually payed to much from an investment standpoint, not because of the numbers, but because we lost access to the capital that we put into the property.

I am interested in acquiring a multifamily property in order to house hack and live in one unit and rent the other unit or units out. 

I would recommend attending as many local REIA events as you can, talk to new people at the events and acquire as much knowledge as possible. 

At the same time, in my opinion, they made the mistake of posting their trainings on Youtube, which allows anybody access to the understand their "SEO tool" (https://oncarrot.com/tour/seo-tool/).I only found out about their youtube videos because I was researching more about them before deciding to becoming a customer.

Also, I first started out thinking that I would acquire the deals using my W-2 earnings only for the down-payments, along with the help of my partners who have W-2 income like me. 

Maybe you can wholesale the next deal to acquire some faster cash without having to use a lot of your own.

I sold both of my motorcycles and used the money as a down payment on my first ever property that I acquired with a traditional bank loan. 

Our overall strategy is to acquire and flip houses in order to generate capital to buy revenue producing properties (apartment complexes ect.)