Thank you! As long as the second night isn't a Sunday you should be fine. The Tattoo doesn't perform on Sundays. Performances Monday through Friday are at 9:00. Saturdays there are two performances one at 7:30 and one at 10:30. I remember thinking we could have even swung the VIP dinner package on that free night albeit narrowly.
I agree with Edinburghlass. You definitely want to view the performers from above if possible. I loved our seats which were high above and under cover but those were only available through the hospitality VIP package. I wanted to be under cover in case it rained. Our seat reservations were confirmed before they went on sale to the public. You can also book general tickets earlier by becoming a Friend of the Tattoo. If you go in August, like we did, you won't get dinner in Edinburgh Castle with ABD. However, if you book the Queen Anne room VIP dinner package with the Royal Military Edinburgh Tattoo you get to have dinner at the castle. The Queen Anne room is the same room for the ABD farewell dinner at the castle for the tours that don't take place in August.
I know some of the meals are included.
What other expensives are there?
Where they other things to do, if for example unable to do the hikes?

The menu is the same at both so don't let that sway you. I had great service at both. I would probably choose The Witchery. 

I know the itinerary has changed quite a bit but this is perhaps the trip I'm most excited about and it's such a joy to experience it vicariously through you! Hello from a fellow Outlander fan (though I haven't read any of the books that were published after Fiery Cross... yet)
Haggis is absolutely awesome, I'm glad you enjoyed it. Have you gone back to Scotland since?