Your question has already been answered but here's my .02...
I moved into my home in December of 2015. It was fueled by propane, which was entirely new to me. When I closed on the house I signed a contract for automatic delivery of propane. Thinking I was secure with that, and not knowing how much I consumed or even where the gauge was, I ran out of propane only 2 months later on a cold February night. We were all gathered around the fireplace (gas) and it went out. It got cold quick. That's when I got to thinking about backup plans. I learned that the fittings are pretty much universal. I have a 1,000 gallon tank connected to my house. In a pinch, I can hook up a 20# BBQ grill cylinder to get things going until the delivery guy can refill it.
I've since converted everything to natural gas and only use the propane for grilling and my hot water heater. I only keep a couple hundred gallons in it at at time and have learned to watch the gauge. I have a pretty good idea of how much I use now.
And on the subject of refill vs. exchange. If you don't know, exchange is a total rip-off. It works in a pinch, but you're getting about 2/3 of the capacity of the tank best case. Most places around here will legitimately fill a tank for less than the cost of a less-than-full exchange tank. You can feel the difference in weight.
You've gotten some great suggestions and advice. Heed it, keep warm and happy travels!