I'm not sure just 500mm of packed section will achieve what you're after, you would need at least 4 plates and the packed section for neutral. If you are looking at building up to a neutraliser, you are probably better off going with the pot still first, then add the plate sections, RC and finally the packed section. This will get you making great pot stilled whisky up front, then single pass great whisky with the plates and RC followed by exceptional neutral by adding the packed section. This is how I built my neutraliser up.
As for boilers, if you have 4" still mount (or fill port) on the keg, cleaning shouldn't be any more difficult than it is for a milk can. Just remember with a keg you'll need to get the holes cut and ports welded on unless you can find one ready made second hand. Oh, and the 5 Star milk cans are sex on a stick.