Welcome to the HW Forum and all the best in your building of a VPO. There are many brilliant minds that contribute here so there is a great wealth of knowledge available.
For starters, let me say that while building an organ might be very gratifying, etc, it is not the only way. By that I mean it does require some (usually considerable) time and even some amount of money. Having said that, you may want to also look into conversion of an existing instrument, many of which have all the needed hardware already and even are quite cost effective. Ebay and some other online forums have listings of used
instruments. The bigger issue there is shipping costs. Sometimes you may find one nearby. Takes some searching.
OTOH, maybe the instrument you have already may be a candidate. It doesn't matter if it is working or not, as long as the (switching) functions still work. Many times, we complete remove all the existing electronics and connect such as the manual "switches" to a MIDI encoder which interprets the switch function such that a computer can respond.
Back to your question as to a guide, check out Ken Spencer's excellent - All About Hauptwerk
http://www.lulu.com/shop/kenneth-spence ... 28874.html
or Timothy Masters - Building a Hauptwerk Organ Step by Step
https://www.ebay.com/itm/Building-a-Hau ... =R40&rt=nc
Either/both can give you guidelines on how to proceed.
In addition there is the Hauptwerk User Manual V 4.2.1 available for (free) download:
https://www.hauptwerk.com/clientuploads ... rGuide.pdf
Hope that helps to get you started. When you have further questions, and you will, post them here and someone should be available to help.
Rgds,
Ed