You can do Lassen in a day if you just want to drive the main road through the Park. Hiking to the Peak is a good hike, about 2.5 miles one way with a 2500 feet elevation change. Bumpass Hell is interesting.
Another part of the Park worth visiting is Butte Lake in the NE corner. (IMHO). Several hikes from there, including the Cinder Cone.
Ample boondocking in the National Forest land surrounding the Park. Current temps are in the low 20's at night and pleasant days in the 60's. However, this time of the year that can change fast.
Many people will post here 299 Redding to the coast is a nightmare, hard towing, etc. I have done it many times and it is not any more of challenge than any other mountain highway.