Migrating from PowerPc to MIPS64

We are considering MIPS64 architecture for our new platform. I have
few questions on migrating 32 bit pSOS bsed application to 64 bit
Linux platform.

1. What are the ramifications of using the MIPS64 in 32 bit mode?
2. If all tasks become processes with their own memory space, is there
any need to have 64 bit pointers?
3. IWhat are the tradeoffs of sticking with 32 bit longs for instances
for 64 bit counters?

- Adwait