I know this can seem overwhelming, and unfortunately There is no simple comprehensive guide. Home Assistant is very powerful, but definitely has a learning curve for new users. I think if you break things down one at a time it will make it easier.
Your first decision needs to be what equipment are you going to run Homeassistant on. However, as the old saying goes, between the options of “cheap, fast, and easy”, you can only choose two. Home Assistant is local and fast- so you have cheap or easy now. You already have a Windows machine, but starting off that way is not the easiest, as you will need to configure a VM, and will likely run into other complications that Windows throws at you around network settings, firewalls, etc (most people using Home Assistant and in IT in general HATE windows). If you have an old laptop or computer lying around, you can install Linux on it and use that, but if you have no experience with Linux that will be painful to learn as well, but worth it in the end.
Home Assistant in its easiest to setup and use form is meant to run as an appliance on a Raspberry PI. You likely can purchase a Raspberry pi for far less then it would cost to replace all your insteon devices and start all over with something else. Here is a video to help choose your hardware.
Next you have to select your install type. Based on your post, I would not recomend container, supervised, or core as they are far too complicated for a new user. You will want the full homeassistant “hassio” which includes the operating system nd addons. That will either run directly on the Raspberry PI or in a VM on another machine (depends on your hardware). Here is another video on install types. I would recommend any of his videos from “Everything Smarthome” to learn more about Home Assistant actually.
Once you have Home-assistant running and setup properly, next you will want to add the Insteon integration. Documentation on that is here
From there, if you want to access Home Assistant from outside your house, or use Alexa and Google to control Home Assistant and Insteon devices, you will have to configure secure external access. The easiest way to do that is Home Assistant cloud aka Nabu Casa. It costs $6.50 a month. Running cloud servers necessary for external access and Amazon skills isn’t free, which is why many “free” services like Insteon, Wink, and Iris eventually fail. There are ways you can configure external access for free, but they are anything but easy. There is a free 30 day trial to test it out.
I would never recommend this route. Most don’t want to offer this service as it is very difficult to configure things remotely. Also, what do you do when there are updates or you need to make changes in the future? You will be far better off taking the time to learn how to do it in your own.