Newbie: OpenLDAP as replacement for Netscape Directory Server

["Koszegi, Kelley" <Kelley.Koszegi@roadway.com>]

Hello,

My organization is looking at replacing the Netscape Directory Server (v.
3.0) that we have been using.  This version is no longer supported and we
are leery of the newest versions because of the pricing structure.  We have
a few requirements and I have been able to piece together some responses to
those requirements from the archives and the administrative guide but since
I have little experience with LDAP (and no administrative experience at
all), I would appreciate a little guidance.  

Requirement #1: able to support multiple instances, either on 1 machine or
multiple
I understand that a master-slave replication can contain multiple instances
on multiple machines.  But can replication be set up to be on the same
machine?  Would it make sense to create multiple instances on a single
machine, and why or why not?

Requirement #2: able to add custom attributes and object classes
I understand this to be possible.  Is that assumption correct?

Requirement #3: robust enough to handle up to around 75k entries on one
instance
Performance in this regard I am sure is related to the hardware.  If we were
to replace a 75K entry single  instance of the Netscape Directory Server 3.0
running with decent performance with a 75K entry single instance of OpenLDAP
2.0.19, would performance be comparable?  

Thanks in advance for any feedback.  Responses to any or all of the above
questions are welcome!
--Kelley