Redbhoy, best of luck with St.Pats whichever route you choose..
FYI, the Institute run an evening class in honours Irish with exactly this is mind [broken link removed]
Also, not sure why you were advised to do honours Maths? IMHO, honours Maths would be a particularly difficult subject to take in conjunction with Irish. In St.Pats the entry requirements are C3 in 3 honours subjects, C3 in honours Irish, C3 in pass English/D3 in honours English, D3 in Maths (honours or pass).