Oh dang that sucks, I would do it if I weren't strapped for time right now. Your timing could not have been worse my friend lol. The best I can tell you is I'm making one album with distorted electric guitar, and doing the same thing with acoustic nylon, so if you want that lol. I would need some real samples of instruments if I were going to do something high quality, unless you would actually prefer to have midi. if you are looking for realism though, that would take for goddamn ever getting all the samples cashed in properly. you would be looking at 100+ hours of work, and you are asking for that from someone's unpaid free time. Once I'm done with my projects, it would take maybe 3 weeks tops if I used midi, because I'd already have the sheet music programmed electronically from paper to whatever program I'd use.. Say I finished my project and used real samples of real instruments, you would be looking at at LEAST 6 months, maybe 3-4 if I finish my project of getting the sheet music on software. The hardest part is getting the samples of a real instrument. Most of the time you have to pay big money for that. The easy part is the actual recording/making of. That's also the LONG LONG LOOONNGGG part though.
Not only that, but the two people (you and whoever would do it) would be a team. Gobs of efficient communication. You might be a strict boss and have a clear outline of the timber. I give you a demo and it has cellos and lyres, then you rant at me that you'd rather have violas and clarinets......you'd have to give the person a clear vision of what you are going for. Believe it or not, but 'orchestra' is one of the broadest genres of music in terms of timbre(instruments that are used). so just saying 'orchestra' is as vague as saying, " Can someone transcribe CT to different instruments than the ones the original uses?"
You might he the kind of boss that says, "try a few songs out and I'll see if I like the mood you are putting out, if I don't agree with it I'll tell you what I'd rather you did on a case by case basis". Generally, free reign bosses can be a dream that turns into a nightmare for an amateur who doesn't know what they are doing. For veteran composers it's heaven, because they can give their stuff a motif, or theme or general mood, without being all over the place and at the same time without being static/stale. You are looking at nothing short of a professional project here man.