Need advise/opinion from the experienced people on my next move

Hello everyone! I Need advise/opinion from the experienced people on my next move. Here is my scenario:

I bought a primary residence.Gained equity in 2 years and took out HELOC to purchase my first rental property(duplex). I don't have a lot of cash left so my budget is tight at the moment but i was hoping to get more rentals. What rout is going to be the best for me? I am looking for the easiest and most efficient way !

a) Convert my primary into rental ( Will have about $300 positive cash flow a month) and take out another mortgage...

b) Refinance my duplex and take some cash out for the next rental?

c) Take HELOC on Duplex(i got denied a lot since lots of banks are only giving it to primary residence)

d) Sell my Primary residence and use the equity for another mortgage down payment on my new primary and buy one more  rental (i ran the numbers and it will be a little tight but doable)

Thank you so much for your input!