A few responses to your queries:

1. If the apps and services you're going to run have 64bit versions then why not go for 64bit guests?  I doubt you'll see any real impacts with regards to resource contention unless you excessively provision memory and CPU to the VM's...

2. Always allocate 1vCPU and then work your way up to additional CPU's depending on bottlenecks.  Sometimes you know in the case of heavily utilized VM's that 1vCPU will be a bottleneck, in that case add in an extra cpu and continue to work your way up as required.

3. You could create a 2TB vmdk for your guest, an alternative option could be an RDM to a LUN on your array?  Perhaps go with a virtual rdm so you can still snapshot the CentOS vm...

4. I'd store it as one large file instead of splitting it, I don't believe you'll have an option to split it into smaller 2GB chunks (perhaps someone can clarify this).  This is also assuming you're using vmfs5 or 3 with 8mb block size.

5. You could thin provision your 2TB disk which will make the backup process faster in the short term.  Perhaps differential or incremental guest OS level backups may be a more feasible way of managing the backup of that vm.

Hope this may help with your deployment