レイアに返事(さん)へ

If you are not familiar with レイア or not so close to レイア, we would call them レイアさん for the polite expression though it depends on the relationship or a peson.
へ (the pronunciation /e/) is almost same to "to" of "to someone" here. When we write a casual letter/ message memo, we often use the way of [name](さん)へ.

将来、画家になりたいの？

Your sentence is not wrong, but you have written other sentences with です／ます style. So if following the style, 将来、画家になりたいんですか？(souns the spoken Japanese) or 将来、画家になりたいのですか？

絵を描く以外、どんな趣味ことが好きですか？

Generally 趣味 would imply the things you like, so 趣味が好き sounds a little redundant.

絵を描く以外、どんな（趣味があるの？/何が好きですか？）