FI 1st!
Yes, its quite OK to do the FI course before the CPL skills test. You must of course meet the FI pre-entry requirements, which include CPL knowledge (ie ground exams passed) 300nm x-country and 5 hours SEP within 6 months prior to FIC pre-entry test. See JAR-FCL/LASORS for full details!
If you do tackle FI first, CPL will be much easier!!