1. It's almost impossible to predict in theory, you should try and measure.
That is because the GW is doing filtering, depends on traffic mixture. For example, a DC that gets 90% kerberos traffic will send much more data compare to one that gets something like 50% kerberos and 50% DNS...
From practical experience I haven't yet heard from a customer that they had a problem with remote sites... Still I advise to carefully check.
2. Unless you have huge traffic there that might add up due to this latency, although I never actually tested, I expect this to still work fine with this latency range.
3. a GW can report only to 1 Center. there is no real benefit of installing multiple centers unless you have multiple forests, in which case the best result will be Center per forest. Sadly ATA does not support multi forest (AATP does).
