But what's the minimum required for 3 point lighting?
And also - do I really need it? I know 3 point lighting is great for creating a cinematographic shot, but how important is it, really? How much will it actually improve my channel? (Yes, I totally think that a good image is important, I'm just not sure about anything more than that)
Find a softer, quieter space in your home. Bedroom? Office/study?
Because you’re having trouble with shifting daylight in the space you’ve chosen, you might want to find a space that allows you to shut out light from windows. Give yourself some control. Or use a window in the background as your backlight if you end up with a key light that’s powerful enough to balance with it.
3-point light may not be necessary. A good key source and a good source for backlight/fill can work. You can get a smaller source to put a little pop in the background if you want. Put a color gel on it to give your background a different ambience. Or if you have something like a desk lamp in the background then use that to add some depth.
As for how much space... even an 8’x10’ room is big enough to light for a talking head. Find a room that allows you some comfort. Style the background by arranging tables, shelves, or a desk in the background. One of the reasons you gave for the space you’d picked was that you can leave everything set up there. That’s not a strong argument for using a poor space. Write down and diagram where and how you have everything set up and you should be able to recreate it easily each time you want to record. Another efficient use of the setup is to record several different videos in a batch so you have mutiple days or weeks worth of content to release between recording sessions.
Backlighting is important because it makes your subject pop. Key lighting is obviously needed. This may be all you need, but the fill would be to help with any shadows either behind the subject, or literally on their face (from their nose, etc.).