So I'm an old veteran of D&D but haven't played in 15 years or more.  I'm looking into the possiblity of starting up a campaign with old friends that live in other states.  is this D&D Beyond what I want to use to host that? If not, what are my options?

D&D Beyond is a wonderful place to house a campaign with everyone's digital character sheets & book access.

For running these games, you will need another tool, such as Discord (voice chat), Roll20, FantasyGround, etc to orchestrate the game session.

If I purchase books on here and the other players join my campaign do they gain access to the books?

https://www.dndbeyond.com/subscribe

Content sharing is included as a feature of the Master-Tier subscription.

allows you to share all of your unlocked official content with other players within your campaigns so content does not have to be unlocked individually.

My friends and I use Roll20 for the map, hangouts for chat (might switch to discord in future), and DDB for rules and character sheets.

The most popular is probably Roll20 because it is free.

I strongly suggest the Beyond20 extension when using Roll20, as you don't need to copy your character info over into Roll20 when using it.

There is also Fantasy Grounds (paid) and Foundry VTT (beta access through Patreon)