First I would like to say that Affinity Designer is awesome and improving all the time, and I now use it almost as much as Illustrator.
As far as I can tell there is no real pathfinder in Affinity, though. It's a very essential function in my opinion, and I hope you can find time to implement it eventually. This post explains what I mean:
In addition, Illustrator has a pathfinder tool that lets you click on intersecting paths and merge them in any combination you like. I'm sure you can understand how powerful and intuitive this becomes when you want to prepare a graphic or logo for production. You can simply select your mess of overlapping shapes and paths and flatten them into something presentable with a single click. Or you can do something like this.