Shiyi wants to make clothes for the marquis and he is as happy as a child 

Yes, it's such a great start for them. When he was sitting at his desk/saw a figure approaching he thought it was Shiyi only to be disappointed with Lianfang emerged. Look at the difference in his reaction when he learns that Shiyi is inside. His excitement is written all over his face yet he's trying to play it cool. I love his friendships with his staff too. It's the highlight of the drama especially when they call him out on his feelings. When he starts making idle threats I can't stop laughing. He threatens one with marriage (General Fu) and the other with service (Zhaoying)...Lingyi can be really petty at times...lol

Actually she suspects someone from the Xu family but she doesn't have a specific person in mind. She's narrowing down her list which is why she's searching his room. She already investigated the women/now she's on to the men.