![](https://lemmy.chiisana.net/pictrs/image/236eaaf8-0ad3-4785-ab46-b8767925bd2a.png)
My understanding is that the “host” instance of the community is responsible in sending things out to the subscribers. As such, when users from B post on a community on C, C will broadcast the activity of user from B to instance A’s federated copy of community on C, and users on A will see the post from the user from B. They should also be able reply to each other’s comments on the community on C.
A couple of years is a life time in tech, but despite that, I think the one thing that should be the deciding factor is if you’re actually going to need the space in the mean time. If not, waiting won’t make a difference. On the flip side, if you’re going to need it in the next couple of years anyway, then it might be easier to recognize that $320 over 2 years is less than $0.50/day… taking the initial hit and take advantage of it earlier will probably work out great.