doubt about houga and youga's exhibition

[kenshiromusou]

Dear friends,
Why our japanese friends use "洋画系公開" when they talk about animes movies?
e.g.: "今度は,洋画系公開の長編アニメになるということで 大 張 り 切 り。"
Which is the difference between youga's exhibition system and and houga's exhibition system?

2- Which the difference between "話作り" and to help with "脚本の段階"?
e.g.:
ぼくも製作の段階から,話作りや,キャラクター・デザインなどで参加してきまし た の で.
b- 今度の作品にも,"脚本の段階"から積極的に参加して.

(Maybe first one means " to write dialogues" and second: "to help in the composition of the script"?)

Thank you very much.
Merry Christmas!!!!!!!!!