Yes, drink normal amount if can. Mix how much is totally up to you. My baby tends to not finish her milk, so I always add half the scoop (equivalent to 30ml) of fm into her solid, to match the amount of fm I want her to have in a day.
Just mix abit till you achieve your desired consistency, I always make 30ml (will have excess cause she eats very little). Yes, normal amount. Usually 45mins - 1 hour after solids.