Hey Rich!
Congrats on our deal! I would first consider the reserves you have for your personal expenses as well as your new business expenses (which many might be unforeseen) before considering scaling.
You said this is a seller finance deal, is it possible to negotiate with your seller or have you already committed to the terms? Everything is negotiable with seller finance, maybe your seller is willing to give you a low or no down payment arrangement in exchange for a higher rate or shorter term? Or deferred payments/interest only? If the deal still works This may be a way to preserve your capital to put toward the next deal. With no bank involved the terms of the structure are dependent on your negotiation.
You may have equity in your home that you can use toward another purchase. I would also consider a partnership with someone who may have what you need. If capital is preventing you from moving forward maybe you can use your new experience in real estate to obtain an investor (friend/family/coworker whoever) to put down your down payment in exchange for an equity/profit split. you do all the management find the deal etc.
There are plenty of people out there with plenty of money who need a place to park it. Real estate is intriguing to many and has so much benefit as you know, but seems unachievable to some. You now have some experience, I would suggest talking to who ever will listen about your real estate ventures and you may be talking to a future partner.
Or continue to look for seller finance or other creative ways to find deals with no or low money down.
There are plenty of books on the subject, including some published by bigger pockets (under bookstore tab)
Long story short, if you have the knowledge / find the deals / and can convince people to believe in you and your deal you will scale as fast as you want.