Hotel-Management like sheet help!

[Tabris]

So, I'm new to these forums and I hope that I'm posting in the area respective to the issue I'm having.
I need to design a work sheet that fully ables me to manage a schedule meant for over 450 people in different hotels in a certain city (a big company move)
So I found that Lists were very useful for dealing with this kind of tasks so I created a tree of lists that depend from the one before that look like this
City List -> Hotel List -> Room List
From the Hotel List you can pick which hotel are you assigning to a specific someone, and after that you assign which room to be used. The room list changes accordingly to the respective Hotel in the list before and so does the Hotel List depending on which city you selected before... and all works beautifully.
It seems like there's no problem, but, it's very important that I know which rooms are already taken and that I haven't capped the hotel reservation capacity.
It's also very important to make rearranging people around hotels and rooms a very easy task because they're prompt to change constantly.
Please help me designing a intuitive way of working this out
I may not be very experienced in excel, but i have some experience in programming so don't hessitate on replying with advanced answers.

Thanks in advance