If your server is only running SQL Server and has no other resource intensive apps running on it reserving 2GB RAM for the OS should be plenty. Therefore, set your maximum memory to 26GB (or 26624MB).
I never bother setting the minimum, but then I don't run multiple instances or other memory intensive apps on my SQL servers. If you do, you may want to consider some monitoring of process | private bytes (in perfmon or process explorer) which indicates the amount of non shared memory reserved by any given process. Then setting a different max for each instance, or a minimum and a max.