Guides - Probably the Basics series that @TheGuySwann has. It's such a complex topic I think it's too tough of an ask for someone to sit down and read a massive article that covers everything, it's easier to hand them half a dozen podcast episodes that they can pick up and put down whenever it's convenient.

Where to buy - I believe there's an episode of that same Basics series that dropped about a week ago that covers this. @River, @Swan, & @strike were specifically recommended while CashApp, and even Venmo and Paypal were included as options.

How to store it - Three stages:

1. Start with a non-custodial Lightning wallet that can also handle on chain transactions. Phoenix wallet would be my go-to at the moment.

2. Once they've gotten enough value on that wallet, point them to a Coldcard and some kind of metal seed backup. Help them as much as you can without compromising their seed phrase or Coldcard PIN.

3. Optional step - If they've acquired a larger stack, consider recommending that they move to a multisig setup from Unchained or a similar company. Lean on their onboarding team who's set up lots of low-technical knowledge people.

Note: If the person you're onboarding is a whale who's going to allocate significant capital up front, it's probably worth jumping straight to step 3.