After I'm done working on the first level, what should I work on first and work on last?

I’m creating a The Battle Bricks fangame, and I am nearly done finishing the first level of the game. Once I am done, what should I do first and do last and why?

  1. Create the title screen and the homepage. (The homepage is going to include the Shop to upgrade and to test your luck on getting a good uber than a rare unit, the Loadout to, well, create your loadout, and the Play button to play the levels.)
  2. Work on the designs of the friendly units and enemies.
  3. Work on the AI of units and enemies.
  4. Create a currency for the game.
  5. Create more levels.

Always work on independent features (features that can exist on their own) before working on dependent features (features that rely on other features to exist). Once you have that priority established, I would say work on the thing you want to do the least, the first. This makes the rest of the work easier.

TLDR: Be strategic with what you work on first, but also don’t put off the harder tasks. Ultimately up to you to decide.