This is my train of thought about iron.

-When going to explore for a swamp, bring along 6 copper so you can put down a forge to make iron nails for a longboat. You will need a smelter of course, but those can be transported by portal. So yeah, longboat first so i can transport all that iron to my actual base.

List of most important things after that
-Workshop & Forge upgrades
-Pickaxe
-Shield
-Mace
-Upgrade them to their highest tier

If you have fully upgraded bronze armor, it should be good enough to at least survive the mountains. Moder i'm not sure, maybe if you are an expert at the game, but any regular enemy should be fine. If you don't have that lvl 1 iron armor is just as effective.

After this, you could go for an axe for wood cutting, but it's all about taste, it's not even the best tier axe yet. A copper axe should be fine really.

Finally, whatever you feel like making and remember, you can always use iron for reinforced chests and iron beams.