The problem with a suit slowing you down is that you will always end up getting nailed by creepers, and without the QSuit's super jump you will never be able to quickly get out of the deep hole you are inevitably going to get stuck in.
A tier 3 furnace seems pretty silly, since we can make nuclear reactors out of the same material we use for tier 2 furnaces. Iridium isnt an especially hard material to work with, its just rare which is why you need UU-matter to get it. I would not mind needing to beat the game before being able to craft Iridium however. Perhaps you need an End stone to craft your first Iridium (only allowed one time), which unlocks the standard UU-matter iridium recipe? This would create an interesting dynamic for Multiplayer as well.