Just to update on this:
Everything seems to be working well on the new host and .net domain
One odd thing I have noticed though is in 24 of activity, the old (.com) forum is getting a huge, for us, amount of guests and some bots. Yesterday for example, 570 guests, plus Bing and Google. The new forum is getting zero guests and zero bots!
I'm guessing the two are related, as in if the bots aren't finding the place, no-one else will be either!
As far as I can tell, I've got the correct settings to allow bots, but now I'm not too sure...