You can just level ur Bernice to at least 50cc40 befor working on Gellius, doing so doesnt need a lot of time and offers solid stats. Bernice is a very good tank and u have copys of her to CR/SU her in future, theres not many situations yet where u NEED an tank thats better then Bernice so Gellius is not in a hurry but still high on the list.
Im a fan of Katie. ... but i guess you could just as well dismiss her and focus on Jerome until u have spare time to care about a second soldier. Katies AW is cute (2% def for everyone) but jeromes is even sweeter so no regards there too.
Spica doesnt always have to be #1 to be awaken. She was my third after Katie (i dont have jerome) and sherry (my team has a lot golds/silvers). What u awaken first should not be "what everyones telling is great in generel" but "what do i need right now to give me an edge?". Once ur core is leveld and u made some expierinces with your team u will notice where it could do better or where you need to make better and there kicks AWing in. U dont AW just for the passive like everyone makes u think, also to make a unit stronger that u need to be even stronger stat wise and that can variey.
I just give you a few examples so u get an idea. Maybe u have problems with maps where Unit Points early in the map is important and lose the map befor it realy starts not because ur too weak but because u have no min cost silvers or the likes. There Charakters like Jerome and Shuka kick in (more likely Jerome). His AW gives u +2 Unit Points from the beginning.
Or other case. (very unlikely one for you). You have a map where u need your tank to also take magic damage while still holding off normal enemys because of reasons, Gellius gains MR after AWing which would solve that problem.
Another one. You notice that your archers arent doing thier job well enough or that u would realy benefit from having even stronger archers, then spicas AW is the go-to option.
You use a lot of gold/silvers or even bronze units on some maps (yes min cost bronzes do get used on some maps)? Sherry can make that whole team get the edge it might need.
You want your Heavys to be even more heavy? (pun intended) Berince AW gives all Heavys 5% more defence.
U need an Tank with so crazy high HP that u dont know what to do? AW Imelia, she gets 10% more HP for all bandits.
Your healing may just not be strong enough and you might need an extra burst-emergency-save-your-live-instant-drop heal? Go AW Iris.
If you see where this is going u get an idea on how to fix for yourself what u will want to AW once your that far. Until then i suggest you to power up your core and gather experience with your units to see what you realy need.
Regarding Shuka im sure someone else then me can give you an better impression if a max cost low skill version is worth it or youll have to wait for an revival.