for the UV map, is it alright to have some unused space in it as the end product, or should the islands take up as much space as possible. Also what reason do you prefer PNG' s for use in blender
is it alright to have some unused space in it as the end product, or should the islands take up as much space as possible.
The general goal is for your UV islands to use as much space as possible. Unused space is inevitable but you want to minimize it.
Compare it to building a table out of wood: If you finish the table and only use 50% of the wood, money was wasted by purchasing too much wood. If you only have 5% of the wood left over that's a pretty good, efficient use of resources.
what reason do you prefer PNG' s for use in blender
There's a wide range of opinions out there regarding image formats. Personally I like PNGs because they can store more pixel information than JPGs while still maintaining potential for small file size. With Eevee I've learned that 16 bit images have a significant benefit which PNG can do but JPG cannot.
PNG isn't the highest quality image by any means but it's a solid standard for textures in my experience.