Town is at maxed population every one is 100% happy now what?

Have you finished all the town projects?

@akard - The meter on the side is the town beauty meter, not the happiness meter. Just letting you know.

No not yet working on clearing the cave

While you're finishing the cave, work on your Museum collections, build up a bank balance, and try installing some Town Improvements (purchased in City Hall). Remember that once you place an improvement, it's there for good, so be sure you're happy with the placement and rotation before you tap the green placement button. (Being able to adjust the location or rotation of a placed Improvement is high on my wishlist.)

Yes, it's true that you should make sure you're happy with the placement of a town upgrade before you tap "Confirm". However, if you decide later that you really don't want it anymore, you can purchase a demolition order from the store, use it on the item you want gone, and voila! If you decide that you want the item back, you'll have to purchase another one.

Working on cirle of stone now, going back in forth between projects

A suggestion: work on one project until it's finished. Each completed project opens certain features of the game, and you can be enjoying those features of the first completed project while you work on the next one. I'm not going to spoil the fun of discovery by telling you what the features associated with each project are. In some cases I don't know or am not sure. The one thing I'm pretty sure about is that I don't know everything that the projects do for you. I'm pretty sure the bridge lets you get into the Northern Lands, for instance (can't fool me!) but if it does other things I don't know.