Thank you for the post!

I've followed Hell Hades and his gearing tips religiously, so while there are probably tweaks I can make, I think I'm on solid footing. I haven't had an overabundance of champions that are even worth gearing, so I guess that helps, too. 

But, we'll see if there are any other tips given, before I do that. I appreciate it!

Try working on your CB team for now imo, that's where you'd be getting your early resources (gear, potions, sometimes some shards and books).

As for arena, running the usual speed nuke comp would be the easiest to work on. You got Skullcrown, so getting to Gold shouldn't be a problem. If you post your roster here we can suggest comps.

First of all, I have good news for you: when the mission says upgrade 2 GH bonuses to level 4, it means 2 total, including the one you already have. You should see once you actually access the mission that it immediately registers 1 of the 2 as done. Of course, you will later reach far more demanding progress missions requiring several thousand gold medals, so progress in arena remains imperative regardless. 

I would also add, to progress in arena you need to take some risks and also attack teams that, at first sight, look quite tough to beat. You probably shouldn't be like me and attack even ultra-powerful teams just for fun and to see how they work, but try some for which you see a small chance to win. You'll certainly lose some of those fights but you'll also win some and in some of the losses, you may be able to spot an alternative tactic that could grant you victory in a rematch (assuming you have some back-up options for your arena team, which if you don't, you should). And in any case it will help your tactical skill and your ability to assess opponent teams. 

Regarding farming, I wouldn't recommend large-scale farming of dungeons at stage 12-13, except maybe during events. You should still be farming food to bring additional champions to level 60 - once you have enough level 60s to work with, you should be able to run dungeons a coupe of stages further (generally stage 16 is where farming starts to be good, partially because from then onwards you can no longer get lame XP brews as reward). You say you have 11 epics in the vault doing nothing - almost certainly, at least some of them could make a difference in at least some dungeons, and possibly some of your rares could too. Also important is getting to the point where you can reliably run minotaur 15, to farm masteries for your main champions, which can make a big difference especially for Clan Boss. 

Because as LXZY said, CB is very, very important and you should always be going for the best chest you can obtain every single day. If you're stuck in a clan where the boss you need isn't open, or open but not getting killed, change clans.