OP here! Thank you all so very much for the replies and advice! There are so many people I want to reply to, but that would take forever. And a few options I hadn't considered before, so thanks for that.
This isn't a once in a lifetime type of trip, as all of my children have been to WDW before, even though the youngest doesn't really remember. However, this will probably be the last Disney trip we take as a complete family before the older kids start living their own lives. That's why I am trying for 2020, but will take 2021 if I have to. There's DS19, DS14, DS8, and a kind-of adopted son that lives with us who is a legal adult.
While I appreciate the recommendations of staying in a rental house/condo, we really do want to stay on-site. The last time we went, we stayed in a wonderful rental house, and although the house was beautiful with a great pool and we saved a lot of money, we didn't enjoy that vacation as much as the previous times when we stayed on property. For us, that magical Disney bubble is real. So for this last family trip, we want to stay on-site.
I also did think about and look into the DVC rental points, which is a great option! That was my initial plan, but given my particular situation, I don't think it'll work out for us, unless I completely give up the 2020 idea and push it to 2021. You have to have the money upfront for the points, which I could have in a few months, but that could lead to other sticky situations. For instance, they recommend booking pretty far in advance, so there could be some hiccups if I wait too long. Also, they don't really do cancellations, so for that option, I'd have to give up the hope of 2020.
The Park Hopper thing. While I understand completely that I could save $4-500 by ditching the Hoppers, I don't really want to. In the grand scheme of things, those few hundred dollars isn't going to make or break the trip. We like the flexibility and freedom it will offer, especially since everyone except the 8 year old is old enough to go and do things on their own. Plus, we tend to do a park during the day and go to MK every night. We enjoy coming down the waterfall of Splash Mountain while the fireworks are going off. We like it when the lines are short because everyone is watching the parade or fireworks, and then take their small children back to their hotel rooms. It's something we enjoy, and going to MK at night is one of my husband's favorite things, so I don't want to give that up for a few hundred bucks.
I'm going to look into the Bonnet Creek thing, which I'm unfamiliar with. Honestly though, I think my safest bet is to plan for 2021, and if the saving goes really well, I shouldn't have a problem booking a couple of value rooms for Jan 2020 even in late fall. You all know how it is though! You get thinking about a Disney trip, and you get all googly-eyed, trying to think of all the different options to get you there. Thanks again for all the advice and help!