As the title suggests I am looking for advice on how to go about selling platinum units and summoning in the current gacha.

First: There is one unit I really want to get from the trade post however she and other useful things alongside her cost rainbow crystals which at my current state are difficult to get a hold of. The only place to get them reliably is through the daily revivals and here is my question. How should I go about selling these units? Some units are intrinsically useless to me such as Revi and Asami so I have no qualms about getting rid of them. But should I try to have a decent version of them and sell the excess or just get rid of the already existing copies?

Secound: With the current premium gacha we have a score of new units coming in and as any other player I would like to get one or two. However my current stock of sacred crystals is at 23. Is it worth it to spend them and try to get new units or save them for another gacha role?

My apologies for the long post.