I recommend dbi (https://github.com/rashevskyv/dbi/releases/tag/336) (you only need the nro app)
You don't need anything other than the app itself on your switch and here is explained how to install from usb https://github.com/rashevskyv/dbi/blob/main/README_ENG.md#run-mtp-responder
I think the most important thing you need to remember is that when you update firmware you always have to install latest sigpatches. If you forget that your games might not boot at all