Remember, smart travellers use the telephone...and internet. Some places in Portugal may be closed or have seasonal or reduced hours of operation over the holidays. It is the off season for most places. Lucky for you, less crowds to boot!
I suggest you check as many websites as you can for specific information. I believe the Castle at Sintra is closed on Mondays? Pls check on that. It's a futile train ride from LIS to find the Castle closed.
The Eden Hotel in LIS is great! It's an old Opera Theatre converted into a Hotel. The rooms/apartments are old converted Opera boxes. Neat, but can drive you mad if you're claustrophobic, after staying there for 5 days!
In Alfama, head up the hill across from the Train station to "O'Emegrante" Restaurant, in the residential area. Or there's another Mom & Pops place just up the hill about ten shops past...it's even better! I don't remember the name, but the owner is Ermalinda and I think her name is over the door with a red light bulb.