You may want to consider a xy-table of some sort for positioning and fine adjusting your subjects. You probably know the workpiece moving table from milling machines and other machine tools. I know macro enthusiasts like the small Proxxon unit, but there are other brands.
http://www.proxtools.com/store/pc/vi...&idcategory=20
The Swedish macro enthusiast John Hallmén has shared quite a few tips and tricks on his web site(s), and he has an impressive gallery of insect/bug images. Alas, I think much of his writing is in Swedish, but I managed to find a variant of his table top platform where annotation labels are in English:
https://www.flickr.com/photos/johnhallmen/6689335483
Note the lens used for vertical positioning by turning the foces ring.