1 - Don't post personal information on social media. Names, addresses, selfies, photos with EXIF data still attached, etc. If you're posting irl photos, take it, sleep on it, and recheck it in the morning for reflections and shit.
2 - Use a separate email address solely dedicated to your vtuber identity that will serve as a nexus for all your accounts.
2.5 - Use a separate browser entirely for your personal life and your vtuber life. I use Firefox for personal use and my vtuber is a scrub who uses Microsoft Edge. This ensures zero possibility of an auto-fill, bookmark, or even social media account logged in yab. (Don't import settings from one to the other, obviously).
3 - Create a fresh Steam account and use the Steam Family Share feature to access games that are already installed on your computer (that you own on your Main). There will be no way to connect your new Steam account to your old account as Steam does not reveal Family Share status (unless you're screencapping the actual Steam window itself, which... why would you ever do that?)
4 - Write down a completely generic and random name that's not associated with you or anyone you know. Day[9]'s was "Felicity." Write that name on a stickynote and stick it on your monitor's bottom bezel. Whenever you tell a story about "someone", you're going to reference "Felicity" (or whatever other name). This is here to help you avoid naming real life people you know.
5 - Google search "Your Name" + "City". You'll find that there's like 20 different 'public info' database websites. They all have methods on opt-ing out and removing your data. Doesn't mean the data is gone, just means that the particular website you requested data removal from won't make it so obviously easy.
5.5 - If you're a resident of the EU, you may be able to take advantage of the GDPR laws and enforce the removal of your personal information from these websites. If you're not certain about a GDPR information removal procedure, do a google search, I'm just some anon and this isn't legal advice.
6 - Create a completely separate Windows User profile for your vtuber avatar and install all your vtuber related programs on here. This will ensure there is virtually no way for your files located on your personal profile to cross over. (Note: You'll have to reinstall all your games, and for Steam, reinstall a new set of games with your main, then Family Share it over to your vtuber account. This adds extra layers of clunkiness but provides a greater level of separation between your personal Windows profile and the vtuber one.) Note that certain games that utilize online play such as Dark Souls 3 and Garry's Mod have scripts that people can use to find accounts that are tied to your vtuber account via Family Sharing. If you are worried about this and want to be very secure, it is recommended that you buy games that use online play directly on your vtuber account.