1) That is one of the big mysteries which can only be solved by building the model!
OK, if you are lucky, the creator states the size or the scale of the model. The scale might give you a hint if you know the real size of the model. If you build real world models such as cars, buildings, airplanes and ships this might be a very reliable value. If you build a SciFi / Fantasy object the scale / size depends on the source the creator of the papercraft based it on. Some sources are good, others aren't. Star Trek models in particular may come in MANY different sizes because the creators of the show themselves did not obey their measurements; depending on the dramatic impact the ships were supposed to have on the audience the makers were very free to scale their models up and down (there are at least a dozen different sizes of the Klingon Bird-of-Prey).
You could load some of the parts pages in Gimp and measure the dimensions of strategic parts. This may give you an approximate size estimation.
2) It depends on the terms and conditions which come with the kit.
In the most cases a recolour for personal use may not be all too bad. However, there may be authors who do not want these to be distributed, so better keep them to yourself if you are not quite sure. So you may start a build thread here but do not upload the recoloured kit to the resource section without permission of the original creator.
3) I use this tool: PDFill PDF Tools (Free) available here:
www.pdfill.com
It is VERY powerful and able to convert pdfs into pictures and pictures into pdfs.
I hope this helps!
