I started off in Washington DC about 20 years ago, but got out of it when the market crashed in '08.

If my primary residence has $500k HELOC, could I use it to purchase a 2nd primary residence and rent out the first one?

Best thing to do is utilize the equity and pull out some cash to buy more properties.

It all works out well when the market is going up and investors are getting paid, but when the market softens and investors lose money, the complaints and lawsuits come in and the dominoes fall. 

somehow this almost never works out; eventually the property sells for something close to land value.  

You should check out the midwest market.

Another option, to echo what @Andrew Steffens said, would be if you're serious about this business it might be worth your time to work with a licensed property manager to learn the ropes, gain some credibility, and figure out if this is something that's a good fit for you long term. 

That being said, there are tons of low cost or free education and networking opportunities out there to learn the business. 

Feel free to reach out if you have any questions!

Check it out: https://www.reimaginehome.ai/The second tool is Cleanup.pictures.