All,
here is the answer from Cisco :
As far as I understand from your case description you are checking which type of FEX should be taken in order to pre-provision your 2248TP chassis. Besides of that you are looking for number of fabric extenders which N5k-C5596 chassis can handle with L3 daughter card installed.
So let’s start with first question. Definitely you are right, at first glance NX-OS gives you not full list of fabric extenders:
dewsbnswi001(config-slot)# provision model ?
N2K-B22HP Fabric Extender 16x10G Module
N2K-C2148T Fabric Extender 48x1G 4x10G Module
N2K-C2232P Fabric Extender 32x10G Module
N2K-C2232TM Fabric Extender 32x10G Module - Zephyr
N2K-C2248T Fabric Extender 48x1G 4x10G Module
N2K-C2248TP-E-1GE Fabric Extender 48x1G 4x10G Module
N2K-N2224TP Fabric Extender 24x1G 2x10G SFP+ Module
Reality is pretty simple here. Keyword N2K-C2248T covers all 48 Tx models except enhanced version (which has 32MB buffer extension). So for your case, this will be right choice.
And here simple example to prove theory above. I do have N2K-C2248TP-1GE which I am pre-provisioning with N2K-C2248T keyword:
TEST_CHASSIS# sh fex
FEX FEX FEX FEX
Number Description State Model Serial
------------------------------------------------------------------------
101 FEX0101 Online N2K-C2248TP-1GE JAF1526CELS
TEST_CHASSIS # sh run | egrep -a 1 slot
slot 101
provision model N2K-C2248T
Regarding to second question I have to admit that with L3 daughter card on board you may have up to 16 fabric extenders (Maximum FEXs dual homed to a vPC switch pair).
Please refer http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/configuration_limits/limits_513/nexus_5000_config_limits_513.html#wp349318 for more information about limits. In fact 8 FEXs limitation was up to 5.0(3)N1(1a). Anyway, your version should support 16 extenders in dual homed config per pair.