You should definitely take on the Spanish. With a little preparation, they can be gone in five, six turns. Their armies stand no chance against your light cav and spearmen if you use them wisely. The Tingi-Corduba trade alone can be worth five grand a turn with proper upgrading! The Gauls are another faction whose military isn't suited to fighting yours. This should keep you occupied and win you a huge power base while not crossing any Romans or Egyptians.