Your database size and number of users should have very little bearing on whether or not you need RAC or Data Guard for high availability. The driver for any HA solution should always be the cost to your company for being down for a defined period of time. Any HA solution will always cost more than a non-HA solution. Since your company is paying for the HA solution, it only makes sense to the company if the HA solution stops them from losing money. For instance, if your database were down for one hour and that translated into $100,000 of lost revenue, then an HA solution would make sense because the HA solution might cost something like $20K or $40K to implement. However, if an hour of downtime only costs your company $1,000, then an HA solution may be more than its worth. It is up to those paying the company's bills or authorizing the expenditure of funds to make this decision. The DBA should lay out the options and pros and cons of each.
OCFS will not work on Solaris. OCFS is only for Linux and Windows. If you run RAC on Solaris, then you can either use Oracle's ASM or a clustered file system from Sun.