529 Room and Board Withdraw

Yes, you can use the average of 12,986 or your rent and food costs, or housing at a local college, whichever is less. 

Yes, if the school is an eligible institution.  You must be a half time or more student. 

As you appear to know, you may use the lesser of your actual cost or the school's  allowance for cost of attendance (COA).  Lacking a COA, I agree with KrisD15, you can use a published average or 

 R&B COA (or actual charges) of a local college, whichever is less.

 To be eligible for using 529 distributions, the course must be taken at "an eligible institution". The school should be able to tell you if it is an eligible educational institution. In general, an eligible educational institution is an accredited college, university, vocational school, or other postsecondary educational institution, including accredited, public, nonprofit, and proprietary (privately-owned, profit-making) postsecondary institutions. Additionally, in order to be an eligible educational institution, the school must be eligible to participate in a student aid program administered by the Department of Education. If they issue a 1098-T they are probably an eligible institution.

Enter your school at the link below, to see if it's on the dept. of education list.

   https://www.savingforcollege.com/eligible-institutions   

Schools that only offer online courses usually do not qualify.  Online classes taken at schools that also have  classroom instruction usually do count.