1—You only pay royalty on the amounts above $3,000 each quarter, so if you make $4,000 you only pay royalty on $1,000
As per the FAQ:
2–You pay Epic 5% of the gross revenue, meaning the amount you would make before everyone gets their payment, so the amount before Valve takes their 30% cut. Though again, you only pay 5% of the amount you make beyond $3,000 per quarter. So if you make $10,000 you would owe Valve $3,000 (30% of $10,000) and Epic $350 (5% of $7,000)
If you are selling the game, then you must pay royalty, it doesn’t matter if the game is complete or not. That includes crowdfunding as well–if you have a reward tier that gives access to the game that you can’t get for free then you have to pay royalty on the value of the game.