Here are some general considerations for a marathon or Dopey:
First off, can you honestly commit to six hours per week of running minimally? Keep in mind, this peak training would occur in November/December for the Disney Marathon or Dopey. That means life commitments with Thanksgiving and Christmas have to be juggled with committing to running at least six hours per week towards the tail end of training. In addition, where you live will impact the feasibility of the training. Because November/December in WI (up north) can be vastly different than say Texas. If you deal with a lot of winter weather in Nov/Dec, how are you going to continue training? Tough it out through the snow, or do you have access to a treadmill? But honestly start there. If you can't realistically and honestly commit to six hours per week of running minimally during that time period, then I'd strongly consider not doing it. Is it possible to complete a marathon or Dopey on less than six hours per week at peak training? Yes. But the vast majority of runners need to hit that minimum, and those rare people who do less typically have more experience in their history.
The next consideration for you personally is whether you'll actually like running. You don't have any history with it based on your post. So if you jump into a marathon/Dopey commitment too soon, you may find you don't actually like running all that much. Then you're going to possibly put a bunch of pressure on yourself to continue something you don't like so you don't lose out on the monetary investment in registration (runDisney is non-refundable in almost all cases). Or, you're not going to like the training, skip out on runs, come into the race undertrained and set yourself up for a potentially serious injury.
Another consideration. I've worked with a lot of runners that come from other modes of exercise (like your indoor cycling, pilates, and walking) and that fitness doesn't always translate to running fitness. So where this becomes relevant is that you have a relatively tight timeframe going from zero running to Dopey in 9 months. If you start out running and we find you're a 2:15 half marathon fitness level, then that leaves us a ton of room on the back end of pacing to potentially comfortably complete Dopey off 9 months of experience. But if you start out running and we find your half marathon fitness to be of a 3:10 half marathon fitness level, then you've got a lot less room for slowing down on race day. So in one case, you could take Dopey at a leisurely pace and finish fine, in the other case if you try and run a similar effort level of leisurely you'll end up getting swept, which means you've got to run at closer to a max effort level which makes things feel difficult. So at this point this is a bit of an unknown for you because like I said other fitness modes don't always translate so easily to running.
Lastly, consider whether a marathon/Dopey has to happen in Jan 2023. Is there a personal rush that you feel you need to do 2023 specifically, or could you wait until 2024/2025? The longer you plan it out, the better prepared you'll be. Endurance running can not be rushed. The necessary gains are on the order of months/years. And sometimes rushing it can only set you back physically or mentally towards the sport. So on two separate paths you could A) rush it, run Dopey, but find you don't like running because of all the pressure you put on yourself and give it up completely, or B) progress slowly in race distances, find a love for it, and proceed to continue endurance racing for years to come. Certainly there are other possible routes, but again something to consider for you personally. Ultimately, it's your life, your choose your own adventure and you'll want to take the path you're most interested in.
Here's some old posts of mine with nuggets for new runners. Some if it is just rehashing some of the things above. Keep asking questions though. This group of people are wonderfully welcoming and full of good advice. Back when I started running I wished I had a community like this to bounce ideas off of. Probably would have kept me from being a dummy and going from zero running to a marathon in 12 weeks. "But it's only $10 more for twice the distance than a marathon. What a deal!" *Head SLAP*
Advice for Newbies #1
Advice for Newbies #2
Advice for Newbies #3
Advice for Newbies #4
Advice for Newbies #5