You have a ton of considerations, boiler size, available power, available cooling reservoir, space/height restrictions, fermenter sizes and more
Available power is the main consideration, a 4 plater 6" bubble cap column can run on low power - see woodducks mother duck
http://aussiedistiller.com.au/viewtopic ... 36&t=11218, but a max speed sieve plate could ask for as much as 6-8kw, more power over that is good for reducing heat up times
Have a look through steampunk 2
viewtopic.php?f=36&t=4639What product are you after? a vm is good at cutting the tails off, this might mean missing some interesting flavors in a rum or whiskey. The amount of reflux in a std vm is determined by the column to valve ratio, big valves are not cheap, so that is the main reason you havent seen such on them on larger hobby systems (or even industrial ones for that matter). CCVM is around, a few members have it on 4" platers with good results and there is no reason it wont on a 6", It can be safely made to go below the 1:! max ratio inherent to vm, here's a unproven design that also incorporates lm in addition
http://aussiedistiller.com.au/viewtopic ... ns#p212819Four plates is plenty for a vm to work, boiler size and power come into play here - over 100L is required, 2-300 being more optimal - this is to ensure there is enough product to fill the plates and have a smooth consistent run. then you need the power to get it to temp in a reasonable amount of time - the 12kw mentioned will take over an hour and a half to get 200l up to temp.
If you go a shotgun rc, more tubes is better, if you go the std vm with a valve you could build it all in 6" and be able to run it either way up, regular cm with the defleg down, flip it and add a valve, now its vm, this would still work with a reducer to 4" as per my plan above