>>9296182E-Hentai has "How to make Anime figures" 1 and 2 for the sculpting side and the Gunpla books on the mecha side. If you feel you need the explanations given, then it´s possible to cut the relevant sections, run them through character recognition and then google translate them. Old scale modeling books generally cover scratchbuilding as well.
A scanner, a printer and something like Inkscape to produce clear, correct and reproducable vector drawings are necessary unless you plan to drive yourself crazy. A CAD software or Blender plus the unfolding add-on will speed up the work enormously.
Doing anything will generally start with research and sketching in pencils or one of them fancy drawing tablets. From that you derive the patterns that are actually going to be transfered to the material you´re going to work with.
Cutting out the parts takes the usual tools - hobby knives, micro saws, cutting shears (oh lordy, these are heaven-sent if you just need to cut consistent straight lines around the outsides of a piece), pipe cutters, punches, drill bits, files and sanding sticks. There´s generally an order to where to cut first in order to deform the sheeth plastic the least, but that´s not something that can be generalized.
If you got a CNC that can work with sheeth material, then most of those tools will become supplementary though.
Assembly mostly requires you to be able to get pieces close to square and there are probably dozend solutions to that. What it ususally takes is a level surface and some precise squares plus something to hold parts in place.
Personally, I use a metal plate, metal squares and a bunch of cube magnets to hold everything, but tape and various clamps are always handy too.
Less of an issue if you´re using a 3D printer instead of assembling your pieces from sheeth material though.
