As long as it's done correctly and you're not discovered, it's very reliable. But there is a lot to consider.
You need to make sure you're not going to be found for about thirty minutes after you begin, as well we include prep time. You need to make sure the rope is strong enough to hold your weight, and when you're unconscious your body will thrash around which can weaken it and cause it to break. You also need to make sure it's tied securely to something strong that won't break. In addition, the noose needs to be one that tightens enough to compress your arteries/airway. Compressing the arteries is less painful than the airway. I believe full suspension is more painful than partial as your weight is being held up entirely by your head and jaw, however it does prevent you from being able to stand before you're unconscious due to your survival instincts kicking in.
If you fail, for example if the rope breaks or you're discovered, brain damage is likely. Depending on how long blood or oxygen supply to the brain was cut off, it could be minor and somewhat reversible or leave you in a vegative state. This is why it's important to test the rope and ensure you won't be found for some time.
As for your weight, I think the biggest thing is to make sure the rope will hold. I'm not sure if it impacts other parts of full suspension.
There is some very useful information here: https://sanctioned-suicide.net/threads/rope.8874/#post-152283 on types of rope and knots.
Best wishes, sending hugs