Being assessed as a couple could leave you better off re tax liability and certainly shouldn't leave you any worse off, how much an impact it would make depends on your other halfs wage. Details can be found [broken link removed] (some further reading can be done on lots of threads on AAM such as this one.)
For credits you should check out this list to ensure you're claiming all your entitled too.
[broken link removed] suggests that you may well be paying too much in tax and/or PRSI. I get monthly tax of €1133 and PRSI of €248 for your salary assuming married couple with one earner, PRSI Class A and just the standard credits.