What Interfaces are necessary for CCNP Lab?

yanks4everontop

I posted this in the CCNA section but I want to build my lab so that I can use it for my CCNP in the future as well.

I currently own:

1 2514 Router
2 2950 Swithces
1 3550 Switch

I need to buy 3 more routers (1 as a frame relay switch).

I'm thinking about the following:

1 2610 w/NM-8A/S as frame relay switch
2 3640's with 128/32 Memory/Flash


My question is, what interfaces do I need for the 3640's. I'll probably get at least 2-3 WIC-1T's but what NM's should I get. The price difference between the 2E2W and the 2FE2W is a LOT. Are fast ethernet ports that important?