Ignore what you’ve been fed by the industry. I’ve never seen conclusive evidence that anything above 150g per day for your typical lifter is of benefit, it’s diminishing returns unless you run a 6 day program.
As for all of your questions after that:
- Yes
- Yes
- Yes
Myself and numerous others here use Huel for fitness and have seen great benefit. As you say, I throw in a scoop of chocolate whey (mainly for taste) and 5g of creatine every morning.
4 x 125g depends entirely on your calorie goal and TDEE.
My biggest shake is:
- 400ml whole milk
- 200g Huel
- 5g creatine
- 30g chocolate whey
- 30g almond butter
That’s around 1300 calories (I think, haven’t checked Myfitnesspal) and is around 1 litre.
What I’m trying to get across is that Huel is as flexible as you make it. I eat mainly Huel but also a tonne of chicken and around 24 eggs a week with a fair bit of veg.
It’s just food, and if you eat it in a caloric surplus with sufficient progressive overload, you’ll gain muscle.