several other experienced players around here main 1 element. usually water. and they do so by rerolling their account until they have some SSR to go with it

as for the wpn vs eido choice, normally you should choose wpn.

as for choosing an element, i would not make the decision until i get an SSR hime and 2 SSR wpn (1 of which comes with the hime) of that element. cause sometimes u dont make choices... the gache choose for you.