Yeah, I'd definitely consider masking up if you're going to be indoors with people while you might still be infectious. Then do as much outdoors as possible.
Though obviously as Sean says it's all miserable advice for a funeral.
Perhaps worth letting everyone know the score as some people may have underlying health conditions that you’re unaware of.
This. Let other people know so they can decide what risks to take.
I hope it all goes okay but remember that the most important thing is the time you spent with your dad before his death. Sounds like he got to live his last days absolutely on his own terms, and nothing can take that away. Even if the funeral can't be 100% perfect, there will be other chances to commemorate his life.