Yes, I would also stick to Antigua and the lake. In Antigua there are so many great buildings and ruins to be seen. Apart from la Merced, Convento de las Capuchinas, San Francisco, the ruins of the Cathedral (just a few of my favourites) don't miss out on La Recoleccion, so impressive. Visit the general market. Consider volcano Pacaya if you have not been close to an active volcano before (it is not a difficult hike).
At the lake you can visit the villages by boat. Go to Santa Cruz and walk to Jaibalito. Great views and villages. Walk from Pana to Santa Catarina Palopo (or hop into a pick-up truck). More great views. In Santa Catarina walk up into the village. Take a boat to Santiago and go see Maximon, visit the weaving museum, see the church and the market. Good shopping in Pana. The nature reserve in Pana is great for a hike (and ziplining). In San Pedro go up the hill to the nice village center. You can consider hiking up Indian Nose.
As for Chichi. You can go by shuttle or bus. Yes, it gets crowded but it is a great experience. But why don't you try the market in Solola (Tuesdays and Fridays)? It is only a 15 minute bus ride from Pana (the bus will be crowded but it is very colourful and only a short ride). You won't see many tourists and the market is fascinating. Just seeing the Maya arrive in pick-up trucks is amazing. The market will be very crowded too (just keep moving) but it is enthralling. Have some snacks like banana bean balls ! And then just sit at the bus stop for some people watching.
