No arguments with earlier posts, some great input there. I just switched from a 6 inch Genie to an 8 inch CabKing as it is easier for my arthritic hands.. But I truly love having a dual 8 inch expando wet sander with silicon carbide wheels. I always start out cutting on the a hard diamond wheel but go to the 220 SC drum to get my cabochon shaped up and remove any flat spots. Then I go to my soft starting with 220 grit wheels.
    I find it so much easier getting my final shape on my cabochon with expando drums. The wide surface and slower cutting allow me to glide across my pre-form cab, remove flat spots and get a uniform domes top. Even with my new 8 inch unit I still love the ease of those big 8 inch wet expando wheels. This realy shortens my time per cabochon and I get a better finish without any hidden scratches that show up during polishing.

I originally had something close to what you are proposing... mine was 100, 220, 600 hard diamond wheels.  What I learned from that was that I was spending way too much time on the 100 wheel.  I wanted something more aggressive for initial shaping.  I also learned that the 600 hard wheel was difficult to get rid of flat spots on.  So, I bought a 60 grit Sachi diamond wheel (8x2) mounted left, shifted my 100 to the center and moved the 220 to the right.  One of the modifications on my E-12 was to convert the right pad to 8x3 expando which I put a 600 SC belt on.  The 60 wheel eats anything in short order, and the 600 expando does a nice job of finishing the shaping and prepping for further sanding and polish.  For further sanding I have a Poly arbor with 2 8x3 expando's that I use diamond resin belts on, and finally I have a homemade bull wheel for cerium polish.  I have been very satisfied with this setup for several years now and have cut a wide range of material.  I don't think there are any absolutes in cabbing as everyone seems to arrive at their preferred setup over time.  Even though my methods/equipment have evolved, I don't regret any purchases, and have enjoyed every step of the journey.

bilqest and lithicbeads thanks for the info and suggestions.

With what I have been reading, an 80, 220, and 600 hard cutting wheels? Then a 600, 1200, 3000, pre-polish wheels or pads?
On the HP b12 I have, I think I might set up  the "cutting" section with three wheels, the 80, 220, and 600. Maybe the  drum can then be the 1200 and 3000? I also have a polishing wheel. I think I might set 600 pre-polish wheel there. I do have the 5 additional 8" polishing pads that could be charged with various grits and polishes. Even so, I think a final polish buffing wheel separate form everything might be good. This would obviously be outside the scope of this machine.

Does this sound reasonable?

Hears a few shots of the saw plexi housing when it was new.
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WOW!!!   

Nice job!!!  My shop is very full. I decided to put my machine on a stand with casters. I can pull it out in a second and use it. Then put it away and get my space back. The stand is a 1950's craftsman tool stand and the top is a 2" butcher block. I'll see how this works when I am done, hopefully very well.

The most important sanding sequence is 600-1200-3000 in diamond , they are the priority. You only need a sintered 60 or 80 hard any good hard 220 of normal weight will be fine as it does not do an extensive amount of work.In the many  years I cut professionally I came to love a metal 600 grit wheel and a 1200 and 600  grit pads on a flat lap for fixing  mistakes.

Congrats on getting such a smokin' deal!  200 for a vintage HP cabber is truly remarkable.  IMHO, HP built the best cabbing machines and should last several lifetimes.  I own an E-12 that I've modified over the years to be my perfect cabber.  I modified the main basin to hold 3 wheels, including 1 sintered, and have had no problems.  I have never replaced the bearings or motor after about 8 years of use.  Someday I suspect I'll need to replace the bearings, but they appear to be standard pillow block.  As for wheel suggestions, start with the fundamentals (100, 220 diamond, to 600 SC) and see where that takes you.  Have fun!

Hears a few shots of the saw plexi housing when it was new.

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I have the B 12 my father purchase perhaps in the 60's ?  I rebuilt it and have some breakdown photos that would be of interest to you. I made a plexiglass hood for the saw with a opening at he right side for my arm and a small hinged lid on the top for visual access. It helps contain the mist. I use water with an additive I purchased from Covington which works tremendously ! Easy clean up and no rusting. The B 12's location in my shop was such that I could not easily use the end leather buffing disc so I removed it, installed a 3" expando wheel and built a housing over the expando to feed water to it and contain and drain the water.
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I make pendants and sometimes re-bolster folding Buck knives so I like to have a wide surface to work on to help me with getting my material "fair". So my expando gets a lot of attention. I have a second older Raytec machine that will hold two wheels so I use it for 80 and 220 hard diamond wheels and also a 10,000 grit soft polishing wheel. The nice thing about the Raytec is that the wheels can easily be interchanged fairly quickly. I have two 80 grit hard diamond wheels. The sintered one is a work horse for fast removal but can create a rough edge on some material so it gets removed and the other metal 80 grit wheel takes its place.

In some cases the hard wheels are just too aggressive so I use 80 grit on the expando and continue using the expando down to 1000 grit.Then to a couple of Nova wheels which are permanent on the B 12. I replaced my polishing buff with a 2" wide felt wheel which I use with cerium oxide which handles the polishing tasks of most of the stones I work with.  Because I make pendants I am directly holding the piece I am working with and need room to move. I could not work with four wheels side by side on the B 12.
I can email you my break down photos if you like or see my back posts somewhere around 12-2018.

Cheers,

Kent

Mechanical abilities will be useful.  I have one old Covington slab saw that likes to act up about once per month just to keep me on my toes.  The machinery can be as interesting as some of the rocks.  Welcome and do paricipate in the discussions. 

Welcome on in!  The coffee and tea are hot.