1) How many virtual router [routing instances] can be created on the QFX5100?
The QFX5100 platform currently supports up to 512 virtual router routing instances.
2) How many VRF [routing instances] can be created on the MX480?
There are a few variables you may want to consider, (both software and hardware) namely the number of routes, routing protocol adjacency limits, and memory. There is very little documentation about the hard/soft limit, but it appears that the MX platform can support a maximum of 8,000 VPLS routing instances. Your actual mileage will likely vary. Read more...
3) What are the differences between the FPC, MPC, SPC and NPC.
A Flexible Pic Concentrator (FPC) is a slot card for MX/M/T series platforms that you can install physical interface cards into. An FPC can also refer to an EX switch or virtual chassis member switch. There are many types of FPCs that vary from platform to platform.
A Modular Port Concentrator (MPC) is a high performance/density slot insert for the MX platform and are either modular or fixed.
A Service Processing Card (SPC) is an expansion card that increases the amount of traffic you can push through your SPU(s).
A Network Processing Card (NPC) directs/buffers/queues traffic between the IO card(s) and the SPC(s).