Aim for 5-10 for medium, 10-15 for large, and 'a bunch' at huge. The random worlds that pop up for you will not have a large number of gold bricks possible to obtain, so I'd look for a rough maximum of 4-5 gold bricks at every small place you go. Also, the bigger the random worlds get the more biomes that are thrown in. 25 gets you medium-sized worlds, 50 unlocks large worlds, and 80 unlocks huge worlds. *Keep in mind you can only access small worlds until you get more than gold bricks. So you need to randomly make worlds for 70 gold bricks. Until you reach 80 bricks, your only way to get gold bricks is to make random worlds. When you reach 80 you can utilize coordinates to locate certain biomes and areas, and when you reach 100 bricks, you'll be able to create worlds based on the biomes you unlocked, and size it from small, medium, large, and huge. And continue to DISCOVER EVERYTHING, while opening a few chests from here to there. Keep a lookout for the items and animals in each biome.
Now, this part is where everyone's voyage will be different.