chienchi,
the answers to your questions are as follows:

Q.will the springs be open on new year's eve?
>>>The Deep Creek Hot Spring is open all year, but only during daylight hours!! It is a day use only area only and that includes Deep Creek as well. No overnight camping at the hot springs!!! No campfires at hot springs!!!

Q.will the roads be ok to drive on given recent weather conditions?
>>>Bowen Ranch is the most difficult road to drive on, on your way to Bowen Ranch / Deep Creek area. The road dirt with many hills and curves on it. After a rain storm the road is muddy and slippery, depending on just how heavy it rains. Drive carefully on it.

Q.do we need to reserve camp space at bowen ranch?
>>>Never.

Q.if so, from whom? is there a number we can contact?
>>>You do not need to call to reserve a campsite or to park at Bowen Ranch.

Q.do we need to reserve a day to hike in?
>>>No.

Q.what else do we need besides the adventure pass and toll fee at bowen ranch?
>>>If you park at Bowen Ranch, which it sound like you are, you do not need to have an Adventure Pass.

Q.what's the best route to go into the area?
>>>Not sure what you are referring to when you say, area. Best hiking route into the hot springs area would be through Bowen Ranch.

Q.where's the best place to camp?
>>>Not at Hot Springs!!! Campsites are available at Bowen Ranch for a small fee.
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>>>Lastly, when hiking into the hot springs, ...... do not bring any glass containers with you. Stable footing at the springs is very difficult and no one wants to sit or step on broken glass.
Bring a plastic trash bag with you for your disposable items, leave no trash or litter at the hot springs.