To provide precision to the answers already provided:
1) Today, go with the UP series. The P series *also* does support 1G speed on the ports, as the UP. For FC you would need an expansion module on the P series.
3) There is the SFP GLC-T which needs 1G speed. for 10G Base-T there is the 2232 TM which supports 10GE Base-T today and you can connect it to nexus 50xx or 55xx.
5) If you are fine by twinax distance, then go with twinax. Be mindful certain nics do *not* support ACTIVE twinax. The cisco switch supports both (active and passive). If you need longer distance, then go with SR. We provide with the FET transceiver if you need optical distance between nexus 5000 and the nexus 2000.
7) To use an SVI you don't need any L3 card, you can use an SVI on the 5010/5020 or 5500. This is achieved with the command 'feature interface-vlan'. If you need intervlan routing then you need the L3 card on the 5500s.