Hmm...

Once you raise the furnace, the order is set.

If you plan to continue, prioritize researching development first. Join an alliance with many active members, no exceptions. You'll get speed-ups and resource support. Hunt beasts and gather resources – that's your top priority. To upgrade only the forge, you'll need to level up the requirements for the embassy, shield, spearmen, and archers. After joining an alliance, low-level upgrades are quick, so you'll likely run short on resources. Focus on hunting and gathering diligently.