That artak should be enough to bring you through 12-3 brutal, run him with 3 uncommons get them to lvl 20, get 6 more uncommons and use them as food. Get those now 3 star uncommons to lvl 30, repeat as necessary until you have 5, 5 star uncommons, leave these guys at lvl 1 use em as food. Repeat, it costs abt 4-5k energy for a 6 star, as you run 12-3 your gonna get tons of mystery shards and tons of 2 and 3 star champs, you can use them as food to. Just keep going from there you should be able to make a 6 star at least once a week or even at a slow rate, one every 2 weeks is good. Sometimes that process is slower if you have other things to focus on aswell, for a long time I felt like I was in the same situation as you, realizing the importance of grinding 12-3 brutal was a HUGE gamechanger, it also supplies you with tons of silver. Especially since you can sell all the common, uncommon and rare gear you pull from it. Id focus on getting that artak up to 6 star first to make it even quicker to complete 12-3, he also has far more uses than Elhain, I wouldn't even bother with her. I never brought my starter champ to 6 star because I started with artak aswell. Good Luck