🚀 go-pugleaf

It seems to me you're talking about two different things here.  You
apparently need the power of a word processing program to create your
table of contents and indexes, and you need to be able to produce a long
document in dtp.

Having done quite a lot of dtp with WordPerfect, I would make the following
recommendation:  Don't even *try* to compose the manual as one document,
but use WP 5.0's "Master Document" feature instead.  Do the whole job as
straight text files to your default printer.  Do not attempt any dtp
formatting until the text is complete and completely edited.  This is as
a safeguard to preserve the integrity of the text document and with no
fancy formatting these files are *less likely* to become corrupt.

Even if you do use Ventura, you'll have to produce your tables of contents
and indexes with *something*.  Once your WP document is finished and
edited, you can then make a decision as to dtp with WP or Ventura.  However,
do not attempt to dtp format your original WP text files--make *copies* and
proceed from there.

Whether you'll want to use WP 5.0 or Ventura at that point depends on how
complex the dtp formatting will be.  If it's complex and includes lots of
graphics and/or charts, I would recommend Ventura.

If you use the "Master Document" setup, speed will not be a problem (and
"speed" is relative to the system you're using anyhow).  I find processing
WP dtp files on my XT to be unacceptably slow (but I do it anyhow).

Remember that your (potential) biggest problem with WP files is the 
possibility of corruption.  You can minimize this by using the latest 
version of WP 5.0 (6/12/89) and by staying in straight text mode until
you're ready to apply more fancy formatting with styles and other dtp
elements.  At that point, remember to *copy* the text files and not use
the originals.

And using text files (set up in the default of Courier 10) are easier to
read and edit.