I feel there might be times when you might need one in the future, especially for male only maps, but up to you.
a mincost elaine is fine, you probably dont need to use too many valks as cc fodder anyway. just try to keep about 2-3 around in case you need a valk for AW or CC fodder.

you actually need an additional tank, but if you dont like using duplicates you can wait until you get another heavy