Cenvat brought forward in new finanacial year ?

yes you can carry forward.

for how many FYs can the cenvat be c/f ?

If you are an exporter and credit accumulated due to export, you can claim refund under Rule.5 of Cenvat Credit Rules 2004. Or you don't want refund, you can c/f to the Current year.

You can c/f "n" number of years.

yes you can carry forward and remember one more thing If you have Credit of Capita goods - 2nd 50% of financial year 2011-2012 you can carry forward in current financial year and utilise too.

you can carry forward provided you are not opting for value based exemption in current financial year, 

there is no such limit of time for carry forward.