Hello JAngeles99 ,
Thank you for your request.
The portion of the journey that will be covered by a bus service is between Milano and Domodossola.
Regarding the difference between 1st and 2nd class, generally, 1st class offers more spacious seating. Meals are not included.
And of course you can travel with your luggage on the replacement bus.
For more information, you can call our SBB Contact Center on 0848 44 66 88 (CHF 0.08/min) or +41 51 225 78 56 (free from abroad).
Have a nice day,
LoredanaD