The hotel looks really good (although too ornate for me... But when in Constantinopla...).
Take your time and don't rush the sights: you can easily spend an entire day at Topkaki. There is a cafe with a view to die for, bring a book, sit in a shade ovelooking the Bosphorus in the palace gardens. Take long walks in the city. I only had 2 days, rushed through everything and regret it immensely. Have to return...
My other 2 cents: stay with azamara. Avoid MSC like the plague (even YC). I enjoyed Cunard more than HAL (in a sense, both passengers and crew in Cunard make an extra effort, and I appreciate that) and there are some benefits to a larger ship (for example, better medical team and its onboard equipment, which is handy (pun) when you happen to break a wrist in Santorini. "Need a cast? Right away... And will send the xrays to our medical specialists in Southampton"). And I don't think you need the Grills experience. Lots of relaxing spaces throughout the ship without having the grills. But 2-top tables may be impossible, and that may be a deal breaker.