You need, VERY roughly, 500 iron per person through to the end of Plains, plus a further 100 or so for the server itself, assuming a single combined base for the players if the base doesnt need iron supports. Thats 6-8 crypts per person depending on luck, so you can do maths accordingly on how much impact the 175 limit may be.
Mistlands itself has sources of iron which should be sufficient for your mistlands needs, although transport may be tedious.

Yeah, the whole minimum size to have crypts thing does concern me. We'll just have to see if they remembered to account for that in their changes.