First of all - we’re really glad you appreciate using Unreal Engine!
As for use of the logo, you need to fill out a separate trademark license.
You mention raising funds, but you don’t say how you will do it. How you do it makes a big difference in whether a royalty is owed. If it’s just a pure donation, no royalty is owed, but if the money is an advance on development or if it’s gets the person who donates access to the game or some kind of in-game benefit, then it is subject to a royalty.
You shouldn’t worry about a donation to Epic - you should invest in making your game as good as possible!