Is this an OLTP system ? the defaults are the best usually when you don't know what value to set. SQL automatically decides when to use a parallel plan and it normally doesnt require any input from the user.

If you set MAXDOP at the server level it applies to all queries executed on the sever, instead I would suggest you had a query hint when needed and leave the rest at defaults.

for an OLTP system you very rarley need parallelism for DW you almost always need parallelism but how many CPUs to use it best left for SQL ti decide.