Vacuform kits call for a slightly different approach,requiring much more preparatory work than a normal injection-molded kit. They are not really difficult, and if you find an interesting subject, by all means go for it. If you understand how vacuform kits are made you'll understand that the 'hardest part' is to sand down the thickness of the sheet of plastic used in the manufacturing process. For aircraft in particular, there is a fine line between sanding too much or just enough to get a decent looking trailing edge on all flying surfaces... Many old vacuform kits are also quite crude in terms of engraving and details, but more recent kits also come with metal/resin/PE parts that will help you along. To be honest, evn if you ever found that 1/72 ID Model kit, I would recomment you starting with something WAY smaller. Large vacu kit also call for many re-inforcing techniques. You want something small that you'll be able to sand down in a couple of hours, not a Galaxy that will require days of preparation. If you are into WWI aircraft, there are many little vacu kit out there that are easy(ier) to build in a couple of days. Aeroclub of England have some decent vacu kits in their range, at various scales, and theirs normally come with lots of extra metal bits. If you like airliners, I'd recommend Welsh Models 1/144 offerings, that come with some vacu parts as well as some major resin bits (wings), white metal and even decals. The best Vacu kit I've ever seen is Echelon's 1/32 English Electric/BACLightning. If you want something big, go for that one.