UE4 has a 5% royalty that starts after the first $3,000 of revenue per product per quarter.

"If I release a commercial product, what royalties are due to Epic, and when?
Generally, you are obligated to pay to Epic 5% of all gross revenue after the first $3,000 per game or application per calendar quarter, regardless of what company collects the revenue. For example, if your product earns $10 from sales on the App Store, the royalty due is $0.50 (5% of $10), even though you would receive roughly $7 from Apple after they deduct their distribution fee of roughly $3 (30% of $10)."

good vids on BGE.. he talks really fast. There are tutorials from other folks in a variety of languages
https://www.youtube.com/watch?v=u-uQqhpXIQA

Thanks!
I dont mind royalties, I am planning crowdfunding, legal expensives, etc.
The hardest part is the start. I have been planning for half an year after my potential teammates in an adventure game just quit.