For fillets I use the following:
Inside the hull and deck for seams and corners, I use thicken epoxy fillet by using Colloidal Silica (Cabo of Sil brand ). You could also us wood flour as a thicker.

The bow and stern end pours/fills, I follow the steps in Nick Schade's videos for using Phenolic Micro Balloons mixed with epoxy. The micro balloons will help reduce the weight vs a pure thicken epoxy pour.

How much carbon fiber depends on the size of the cockpit and how many layers. For me, my cockpit was a larger cockpit, 35 x 19 inches. I bought three yards and used about a third for two layers of carbon fiber on the coaming per Vaclav instructions, which are excellent.. I would be safe in getting a couple yards. I used the extra carbon fiber to lay bracing strips under the deck on the back of the cockpit.