-You need an OS user as well. We have helped many customers with 3rd party service providers, this is usually a manageable hurdle. SSH key exchange, and use of the "oracle" user, can remove the need for your service provider to provide a password or create a new user.
-Delphix currently supports UNIX to LINUX conversion. "UNIX" includes Solaris Sparc, HP-UX, and AIX. Solaris on Intel is currently not supported, but it might work.
-Even over long distances, we typically use the network. The initial runtime might be many days, but the impact on production is minimal. If required, you can ship a tape, build a standby, and use that for your initial sync.
-Subsequent syncs of 400 GB/day over 12h would require a 100 Mbps pipe. Typical compression rates are what you'd expect: 2-5x and depends on your data. NB: the pace of change can be hard to determine...a single block changed 100 times will only be shipped once to Delphix. The amount of archive log files is a rough indicator, but can be much, much larger (or, rarely, smaller!) than the changed blocks pulled by Delphix. The size of an incremental backup is the right thing to check, not your archive logs. A true change rate of 10% on a database that large is rare, while 400 GB of logs is easy to believe. Your change rate, expressed as unique database blocks changed, might be low enough for 10 Mbps to work.
-Server sizing and topology shouldn't be done on forums. Delphix is both vertically and horizontally scalable. Our solution architects provide scripts and expertise to help you determine the right server sizes and topology. The server you described might work, but then again it might not.