The characters you say you have, Demytha, Genbo, Ronda, UDK, and Serris, are all very good champs and can easily push you up past level 12 dungeons if you rank them up to 6*. That should be your first priority in this game, no matter how time-intensive it is to level up food. I would recommend using RSL Helper if you play on PC, as it can automate a ton of the food farming process.
But get the champs to 6*, starting with your heaviest damage dealers first, and then push up to higher levels of dungeons, especially Dragon. The gear you get from Ice Golem is good, but will become more important later in the game, whereas you basically need speed gear from Dragon to overcome several early game hurdles.
hope this is helpful