Dude. Calm down, take a deep breath. You are excessively worrying about things that aren't worth worrying about. I know its stressful and competitive but you are overthinking this in my opinion. It really doesn't matter when you rotate with your home program, you will be on a learning curve no matter where you are at but if you are competitive for ortho you should be able to pick it up no problem, you will just need to read more since you didn't have a 3rd year rotation in ortho. All of the things that apply to your surgery clerkship will apply to your ortho sub-Is.
As far as which service to rotate on... most people say trauma because it is where you see the most and get a good feel for what I consider to be the nuts and bolts of ortho since you see a little bit of everything. However, if this guy wants you on his service and wants to write you a letter you should go for it. You have no idea how far a good letter of recommendation goes is this field, especially if he is a fairly well known guy. It seems like on the interview trail all the hand guys know each other, all the trauma guys etc. The letter may be the most important thing you get out of your sub-I with the exception of knowledge and finding out if ortho is right for you. No one knows what services you rotated onwhen you interview unless they ask you and even then it won't matter which ones you were on. I've been on trauma, hand, joints, sports and tumor during my 3 aways. It doesn't matter which service and doesn't change your application one bit. A letter on the other hand does.