The bouzouki gets its sound from the pairing of strings (courses) and Greek bouzouki players I've met (3) seem to tune them as GDAE like a mandolin. Or rather, an octave mandolin.
Your CGCGCG sounds more like a Cittern tuning and getting the 1st string (normally E) up to a G is likely to be a big problem. Try A-E-A-E-A-E. A lot depends on the instrument's intonation. Try (strings 1-6) .012 plain, .016 plain, .032 wound, .042 wound, .053 wound, .065 wound.         
I found a pair of 5-up machine heads in a flea market and converted a cheapo (Lotus) classical guitar to a five course guitar/cittern by redrilling the holes in the head to accomodate the machine heads, adding four more holes in the bridge and refiling the nut and the bridge for ten strings. I tuned it EE-AA-EE-AA-EE. Depending on the strength and construction of the instrument you plan to convert, you'll have to experiment with string guages, but use no more than .009 on the high E strings and no more than .030 on the low E strings to begin with. The width of the fingerboard on a classical guitar also gives you room to accommodate ten strings.
I later acquired a bouzouki which I tuned AA-EE-AA-EE and two years ago I got an octave mandolin (AA-EE-AA-EE) which has a much fuller and louder sound than the guitar/Cittern or the Bouzouki. This tuning gives a natural key of A major and sounds very modal (Celtic). I've also found Phosphor/Bronze strings give a nice bright sound.   
To change keys, capo 3 is C major, 5 is D major, etc.
Hope this helps.