THERE'S NO SHORT CUT TO A PAINT FINISH, sand and fill hull to good finish then spray with car primer aerosol ,when dry sand and fine tune any blemishes,
do this a least 3 times . you should now have a fair finish for final spray colour , my tip is to paint a thin coat of fibreglass resin with a bandage on panel joints.
as for battery position to stern to lift the bow this will help the boat to get on the plane , as John said try and get the receiver above water line and has much aerial exposer .
also you could fit a false removable deck to stow gear see my pics there's room its all about forward planing hope this helps.......LARRY....