Prosperous webeindustry And in saying that, you wouldn't experience noticeable performance issues with more complex forum software such as IP.Board or phpBB in our day in age. 70,000 posts and 2,000 registered users is by no means a large community when compared to others out there.
ahrasis The possibility is there but there is no point thinking about it yet as flarum is still in beta and require ssh which not many shared hosting support. You may try it using whatever data you can convert but I doubt you will be satisfied until its stable release finally comes. So, no recommendation until then.