On the topic of selling 5* characters – this is a mixed bag.
On the one hand, 5* are tough to get, take up space and they
are an extravagance and may sit with 1 cover for a long time.
On the other hand, their relatively high health at low
levels and high match damage can help. If you are able to run a team that produces
strike tiles, such as 3* Blade that match damage can stack up. A non levelled
5* can match damage to death easy PvE rounds and also the Dat Required
character portion of DDQ in super quick time saving your other characters for
tougher later rounds.
If you don’t level them too high then you can comfortably
keep them rostered whilst you build your 3* tier as boosted 3’s will scale