I might be able to provide something of an answer for you by examining Henry VIII's court. Now, I do understand that his reign was slightly later than what you're looking for, but in many ways--especially in matters of personnel and kitchen technology--there would have been a lot of crossover (I'm just using Henry VIII because I happen to have a book handy that details his court's food production in a way that I think might be helpful for you).

Okay. Obviously Henry VIII had a lavish court, and his kitchen reflected that. At any given time, the kitchen as many as 350 people working to feed 700 members of the court. This does not include actual feasts, when the kitchen would hire so many temporary workers that they would erect temporary "kitchen tents" outside (I don't have exact numbers for how many temporary workers would be hired, though they would come from the surrounding city/town). Ovens as large as 12 feet in diameter could make hundreds of pastries or pie crusts at a time. While exactly how many dishes any individual at the court had available at any given meal varied based on their importance, even servants had four dishes at each meal (the Lord Chamberlain had sixteen dishes at dinner).

Kitchen technology, such as it was, wasn't much different for the wealthy than for anyone else. Kitchens relied upon vast ovens and cooking things over fires. Meat would be roasted on spits which young boys would turn for hours, to make sure that it cooked evenly without drying out. Of course, the wealthy would have the best cooks and best ingredients, so that certainly made a difference.

This is to give you some idea of how vast an operation Henry VIII's kitchen was on a day-to-day basis, to make it clear that, yes, a kitchen of that era could serve hundreds of people on a daily basis. And feasts were another level of excess. Henry VIII spent around 4 million pounds annually on feasting. These feasts had up to seven hundred guests and 240 (yes, that zero is supposed to be there) different dishes.

The Field of the Cloth of Gold, a summit between Henry VIII and Francis I, is an example of even more lavish feasting. At this event, one of the most opulent of its age, Henry VIII brought with him a retinue of just under 4,000 people, and Francis I brought similar numbers. To this summit was brought the following amounts of food to be prepared by Henry VIII's traveling kitchen staff: 2,200 sheep, 1,300 chickens, 800 calves, 302 herons, 13 swans, 17 bucks, 7,000 whiting, 700 conger eels, not mention all the non-meat food items like sugar and flour. This was, in today's money, 2,651,700 pounds worth of food. Twelve pastry cooks, twelve brewers, and twelve bakers were hired in addition to the king's usual kitchen staff. This summit lasted nearly two weeks and food was provided for thousands of individuals during this time.

I hope this somewhat answers your question. In short, yes, feasts of the magnitude shown in A Song of Ice and Fire were certainly possible.

Source: Weir, Alison. Henry VIII: The King and His Court. Ballantine Books, 2001.

Note: I'm aware Weir's book was written primarily for a popular audience; however, it is also very historically accurate. I used this book in a graduate seminar taught by a professor whose speciality is Renaissance England, and he touted this book as an excellent resource.

Are there any good places to find accurate recorded recipes from ancient periods?

A bit after this time but to anyone interested in archaic cookery I strongly recommend Alexandre Dumas' (the same) Dictionary of Cuisine. Lots of lost cooking forms from a similarly lavish dining age. Example: the now extinct subspecies of terrier known as a "spit dog" whose sole purpose was to turn roasts via hamster wheel mechanics.