Enterprise readiness - mirroring / incremental backup solutions?

I'm currently starting to evaluate Open Source RDBMSs for use in a
high-volume, high-availability environment.

My main requirements are:

1. Ability to store approx 200Gb of data, with about 5Gb of data
changing per day.

2. Support for high number of concurrent short transactions under
REPEATABLE READ transaction isolation with row-level locking (or
equivalent optimistic concurrency control).

3. Fast (i.e. < 5 mins) failover time to a constantly mirrored secondary
database server.

4. Ability to perform continous network backups such that in the event
of both the primary database server and mirrored database server
suffering total failure, no more than 1 hour of data is lost.

First impressions are that PostgreSQL (and SAP DB, but definitely not
MySQL) appears to meet requirements 1 & 2, but I'm not sure whether it
(or any Open Source db) can currently meet requirements 3 & 4.

My understanding is that while PostgreSQL offers hot backups "out of the
box", it only offers full backups and does not have built in support for
mirroring. Clearly, backing up 200Gb of data hourly is not feasible.

Are there any third part solutions capable of making PostgreSQL meet
requirements 3 & 4?

I'd imagine it may be possible to satisfy 3. using file system level
mirroring, but I'd appreciate it if someone could confirm this.

My last question is somewhat pie-in-the sky, but assuming that
PostgreSQL cannot currently meet requirements 3 & 4 even with 3rd party
solutions, what are people's gut reactions to whether a small team (e.g.
5-6) of experienced, full-time paid developers could add mirroring and
incremental backup support to PostgreSQL within 18 months?

Cheers,
Kieran Elby