is storing order_id via paypal payment really nece

Question

I am using paypal gateway. I am using js sdk smart payment buttons.

Question 1) Turns out that when I make a payment through js, it returns me id and capture_id(id means order_id and capture_id means transaction_id). Then I use webhooks to catch events on my back-end. Looks like it takes me lots of parsing 'links' property in it to get order_id. Is it really necessary to have order_id stored in my db? or capture id is enough to do anything?

Question 2) when events arrive on my back-end, sometimes they arrive 2 times or 3 times. (Same events). Why is that? I acknowledge receiving them via return response('', 200); but still, this is not enough. Any ideas?