If your ATS is going to be ahead of the Main, you'll need to have an ATS that's rated "Suitable as Service Equipment".
Also carefully watch your system grounding.
You will definitely need an outage in order to do the tie-ins; how about seeing when the hotel could best tolerate it.
I would think that the majority of the guests would be out of the hotel after 10:00 in the morning and the power would need to be back on by early afternoon to give the HVAC a chance to catch up with the stale air before everyone comes back for the evening.
Do everything that you possibly can before you shut down; and you will be a real hero to the hotel if you can get the power restored before your scheduled deadline. If you figure that your crew will need a 3 hour shutdown, tell the hotel that they will be down for no more than 4 hours and prepare to receive their accolades when you get back online an hour early. I would recommend that you use extra crews if you need to in order to minimize the total downtime.
