Buying a refurbished unit comes with risk regarding 1.) if it works and 2.) if it is truly unclaimed.
Yes - a license is required and they come in 1, 3, 5, 7 and 10 year durations:
LIC-MS225-24P-1YR
LIC-MS225-24P-3YR
LIC-MS225-24P-5YR
LIC-MS225-24P-7YR
LIC-MS225-24P-10YR
The 10Gig SFP will depend if you are doing multi-mode, single mode, etc:
MA-SFP-10GB-SR
MA-SFP-10GB-ER
MA-SFP-10GB-LR
MA-SFP-10GB-ZR
I'd encourage you to look at the MS130-24X or the MS150 series as they are both "newer" units with a bit more longevity down the road.
MS130 Datasheet
MS150 Datasheet
At some point MS225 series will become EOS/EOL.
I personally would not recommend buying a refurbished unit.
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