Onboarding emails in like a drip campaign style aren't really something available in the core itself. I would suggest using Zapier to connect with MailChimp or another drip campaign / automation designed email platform that can handle this for you with ease.
Outside of that, Announcements and Alerts can be tailored to a member group so could be like a "Welcome message" and then point to a specific topic, page, whatever on your community which has more onboarding resources. I have something similar on my community where I have an alert welcoming them and then direct them to how to post photos and to introduce themselves to the community. The bad news is there really isn't a drip style to send 1 notice on day 1, the next on day 2, the next on day 3, etc...