He turns into a perfectionist when he gets into things.
①He goes overboard when he's hooked on something.
go overboard→やり過ぎる
be hooked on→○○にはまる
②He turns into a perfectionist when he gets into things.
turn into→○○に成る、○○に変わる
perfectionist→完璧主義
get into things→モノにはまる
「彼、トマトパスタに飾るバジルも、パンのイースト菌も全部自分で育ててるのよね。凝り性なのよ。」
→He grows his own basils for pasta and makes his own yeast for bread.
少しでもご参考になれば幸いです。