I don't believe the TA can "pick up" the reservation you put on hold. You'll either need to complete that one or cancel it (or let the hold drop), so I'm not sure there is any value in what you suggest unless I'm missing something. If you want control of the initial booking process, book it yourself (with or without a hold) and pay the deposit and then transfer the reservation to a TA within 30 days; just be aware that some TAs offer reduced perks/OBC on transferred reservations.
Enjoy your cruise!