After selling one and using a 1031 exchange to buy a fourplex in Chicago, he reduced his interest burden by 20% while boosting his net incomes by $1,500 per month.

Philly has a ton of opportunity, but since you are new to the area, I would suggest waiting six months before you buy anything there so you can really understand the block construction of the area.

I am a buyer - my buy box is 200k ARV, all in $150k after repairs, rents for $2000 per month.

In 2025 does it make sense to build a 4plex and house hack it or is it better to buy existing multi-family? 

Notice how they presume they are going to buy the asset at a substantial discount from the lender.  

Starting with a $100K headstart is more than a enough to buy a new primary home. 

Why would an investor buy a $235,000 property that is renting for $1,400?

@Kris TohovitisI wouldn't recommend using your cash to pay off the mortgage on your primary residence since you can likely get a better return on that money by investing it.What's your buying criteria for the multi-family property?

If you buy less or take cash out you will pay tax on that amount. 

You mentioned buying a fixer upper with your HELOC and now are talking about a 20% down payment.