Understanding EA and cross progression

I've been trying to figure this out. I got an EA supporter pack directly from the POE site and plan to play on my PC. Would I need to buy a separate support pack from the Xbox store to play on that platform? When I go to the Xbox store right now, the only way to download it seems to be to purchase a Supporter pack there as well.

Also, what exactly is shared between the accounts?

- Characters
- Stash
- Cosmetics
- Coins

I have tried to look for information but there seems to be a lot of different answers around this.

Thanks.