You'd need about 3/4 cup of granular but I would not use anything erythritol based.

what can you replace with the stevia & liquid monk fruit and how much?

You can try that, but I haven't tested the recipe using either. However, psyllium eggs have worked out well for me in other baked goods.

I find the vanilla is a flavor enhancer. You could leave it out and add a touch more sweetener.

I'd say start with 1 cup and add up to 1/2 cup more depending on taste.

You can. You'll just need to convert. It's a little more than a half cup of sugar equivalent.

You can replace with stevia liquid which is twice as strong (so you'd use half). Or, you could try adding in 1/4 to 1/3 cup of another low carb sugar replacement.