there is a document listed in the resources channel of the community discord server that explains the setup: https://docs.google.com/document/u/0/d/1niBjfAFe2IUh713vHxRP-tFAeB5IqS_EymiaYsF9BTQ/
there will be a more thorough guide out eventually, but it's not finished yet. also you're going to have better luck getting timely and accurate responses if you ask in the discord server, and the resources are much more accessible
The SRC forum doesn't typically work well when people have questions. For a more accurate and timely response, please join the Banjo Speedrunning discord and ask there instead. Here is a link to join: https://discord.gg/5AjXe4Y
You can also visit the website for some more information at https://banjospeedruns.com
any% is several minutes faster on xbox. currently the respective WRs are ~6.5 minutes apart. if you want purely the fastest version, go xbox. you can also take a look at each console's route for ideas on which you might like more
you can use whatever you need for timing. most people use livesplit, but a phone is fine if that's all you have available. a mod will double check your submission to ensure accuracy