Avoid NM, your goal should be to get a 6star champ so you can get more 6stars faster by farming 12.3 brutal.  Unfortunately that is the most important part of the game for progression.  You should probably do nothing but farm campaign with just Kael and 3 food for the next month.

Finishing Nightmare campaign is something you do way later in the game - like, I've been playing almost a year, can auto all dungeons at 20, and I still didn't complete Nightmare. 

But as for grinding to 60, you really should've done that already quite a while ago, some people have their first champion at 60 within a week or two... in any case, you'll need to be doing much, much more of it. I'm at 22 level 60 champs now myself and I'm still not quite what you'd call endgame. 

Oh geez. Well makes sense but its ugly.  I understanding farming 12.3 brutal for silver and XP. A couple of questions:

1.  I still keep doing dailys and monthly for the shards? Right

2. Should I worry about farming gear, the occasional IGP for good off/def/crit/spd gear? Or do I just level champs w/ the mid to crappy gear I have so far until I have a good assortment of 60's.

3. Should I keep schlupping through arena or just enough to get dailys? I've been spending a lot of siler upgrading 3-5 star rare and epic gear so I can farm 12.3 with one main champ and some foods. Also trying to progress in Arena. Now that I can farm 12.3 should I just do arena for my daily's and not worry about gear upgrades and Tavern?

Thanks.

1. Yes, do daily/weekly/monthly/advanced 

2. No, you probably just need to better equip Kael and farm more chickens until you can do Dragon13+/IG13+. Probably farm in 9.3 to get Warmaiden and keep farming there for books, she might be a better next rank up then your epic choices

3. Do as much as you can in arena.  HK, WM and Kael is a good start

Nm campaign difficulty is extremely difficult, you need champs who aren't magic based and bring utility's. That being said even doing three stars on brutal is not