Board Thread:General Discussion/@comment-50.83.126.169-20140604224009/@comment-108.250.40.22-20140605060415

You can still upgrade cards once they reach the max level. The card just doesn't receive any experience, but it takes the arcana boost. Technically it would be best to start feeding it arcana from level 1, to save on gold, but odds are you won't have the 40,000 medal needed to buy the arcana needed right away or that many normals to feed it. I suggest HSR them, the right way using arcana succession, then max level (with slimes) then over time feed it arcana.

Also just wanted to say that the relationship bonus transfers over when they evolve, so no need to max friend both of them. Although though it doesn't carry over for amalgamation.