Regarding sets, yes, it does involve the number of unique pieces they're connected to. Buildings in sets provide all the cool extra bonuses only if they're connected to other unique Buildings of the same set. For example. if you place the Piazza Mask Vendor where it's supposed to be in its set (while also completing the full set), a +4 or something will appear above it, showing that it's connected to 4 unique pieces of its set. The other Buildings it touches will show a +1 to show that they're receiving the bonus from the new piece.
Now, the Town Hall... The Town Hall produces a base amount of Coins every 24 hours, and it can also produce Forge Points along with it if the player is in a Guild of at least level 10. However, with the introduction of Cultural Settlements, you can obtain Emissaries that reside in your Town Hall and can produce other things. They include more Coins, Supplies, Medals, Goods, more Forge Points, and Units of your age. Collecting from the Town Hall while having one or more of these Emissaries active will also show the number of that resource collected along with the Coins and Forge Points.
Hope this helps, but if it's still not clear, tell me and I'll do my best to clear it up.