I'm super interested in speedrunning this game after 100% completing the content the game has to offer, are there any starter resources, route docs, a discord server, etc? I haven't been able to find anything.

There is a discord server you should check out, the link is right under the game title. A great way to get started is to check out the people already doing it and see what they're doing. Watch all the runs you can. There are a number of great players to look at. Cardinal, RaineBT, R5 on the PC side. MoltenAMF on the console side. Are you playing on console or PC? Right now the console side is more active. You can find all these guys on Youtube. I got 2:02 today, I am on youtube as well. If you have specific questions you could ask them in the discord. Are you interested in NG or NG+? Happy to hear about someone else interested in the game. You're very welcome and I'm sure any of the vets would be happy to help you learn about the game. Routes and builds differ, but there do tend to be better ideas than others. It's exciting to see someone else wanting to run the game, the more the better. KKBerry is another player running the game on console right now. You can see his recent 2:03 in the NG+ Discord channel.

discord is the best for asking questions but i can also answer any here if you'd like.