Actually that more or less depends on if they need more Kami to make at least 2 suitable teams...
After that, then I'd go ham on inventory space considering there's a lot of magic jewels you can get now
Except for I managed just well for a long time with just 150 weapon and Eidolon slots, so it may depend on how much stuff you collected. Regardless of the method though, you'll still cap space eventually cause you'll want the space to hold all those event SSR (I now have 270 weapon slots due to this and about 170 Eidolon slots)
Yeah, cause I normally feed R eidolons as exp fodder (along with N)
Now I don't even need to go that far and they'll soon just speed up the process of getting the kaisers