Can freeRADIUS provide everything that TACACS+ can so that I need only install/configure freeRADIUS.
This really depends on the network kit and the Vendor that produced it. Cisco claim that many of the features of TACACS+ can be replicated using Cisco VSA strings. The wiki has bits and pieces for Cisco http://wiki.freeradius.org/Cisco#Cisco_VSAs.
HP Have limited support for RADIUS; You can be an operator or manager .... But you can't really have fine grained control over what commands those users can issue.
Bottom line is TACACS+ generally has better support in terms of fine grained access control, but TACACS+ server implementations do not have the flexibility and range of features FreeRADIUS does.
Much of the kit we are using IS Cisco. So I am guessing I would be best to allow RADIUS & TAC+ to interface with LDAP. Thanks for that :) David