I think the next best step is to take Jerusalem, doesn't look like there are many defenders there. You should also send your northern warriors to grab all the goody huts. There's one in portugal, one in denmark, and one in sweden. The shrine is capped at +20 gpt by the way. You look OK stability-wise.

in Thebes at pop 3, working stone, marble and copper. It might be better to build the Oracle there and let Athens build Work Boats and Colossus followed by Phalanxes/Triremes for defense. Have the Egyptian worker hook up the copper ASAP, then cottage those floodplains. As you get bonus stability from a growing GDP, cottaging Thebes should make up for it being in the red stability zone.
for all enemies. Caste System is not needed because honestly, with all the wonders and +150% birth rate you get tons of GP with greece.