Okay, Here's the jist.  at your stage, you should be keeping all Legendary and Epic Champions (they sometimes get buffed) and dupe rares for faction guardians.  Your chickens (sacrificial lambs) should be common and uncommon champs that you've upgraded to the point that they are ready, no masteries, no artifacts, no ascension.  Just bare champs.  There are two primary Uncommons that are useful. Armiger and Saurus.  Keep them around, you'll want both of them at 60 eventually.

You want to figure out who you want to rank up to 60 and dedicate that week to getting them there.  Getting a stable of 50s with no 60 is definately holding you back.  Priorities should be a 1) Campaign farmer (a champ that can take on Brutal Stage 12 (Brimstone Path) level 3.  This is the best experience + silver per energy spent. Sell all artifacts you get from here. 2) Get a good team of 60s together to take on the Dragon, early stages are basically whoever you have, later on (14 and above) require more specialized teams. 3) If not already, join a clan and gain access to the Clan Boss Demon Lord. The rewards there are beter than most locations.  Don't let looks get in the way of a good champ.  Revivers and champs that can cast decrease defense may not look awesome, but they are incredibly valuable.  FOllowing the missions for arbiter and then ramantu later are very important as well.

So for Galek, you should get four 4* uncommon chickens to rank him up to 5*.  Then do the same thing again getting five 5* chickens to rank him up to 6*.

Your focus should be on stage 3 of whatever your highest level of campaign is.  Eventually, Galek should be able to take on Brutal by himself (solo) with three "chickens" in tow. don't worry about them dying, just keep Galek alive.

If you can upload a screenshot of your roster, it will be easier for people to assist you in determining who you should keep for later and who you can use as chickens.  Also, Hellhades has great videos on who to keep and who to burn.