multi region EC2

[Deno Vichas]

all,

we just about ready to push our app live and just have some cassandra 
tuning left.  i've been currently running a 4 node (rep factor 3, 
simple) in EC2 using the datastax AMIs (thanks datastax).  so after 
reading through a bunch of docs i have a few questions.

 - what is the min and recommended number of nodes to use in multiple 
region cluster.  we only have a single app server right now.
- can i migrate the replication strategy one node at a time or do i need 
to shut to the whole cluster to do this?
- what type of performance hit am i going to take having my app server 
cross regions to get to a node.  coming from the SQL world, this is 
usually not a good thing.

if i was to stick in a single region is the any best practices for 
backing up a whole cluster?  from the docs it looks like i need to 
snapshot each node one by one and then copy off the snapshot to 
somewhere offsite.


thanks,
deno