There are a couple of poser python scripts that add 'realism' nodes and whatnot to spiff up skin textures. Bagginsbill has one that is free. So you might want to look in that direction to update older textures.

Are you remembering to Magnetise yoiur V4 clothing? she has built in joint deformers you have to apply to the clothing so it behaves as its supposed to. if it still doesn't fit in default shapes, then you need to look at fix morphs and whatnot

As far as scaling parts goes .. poser has never done well with conforming items after scaling parts. that's something you're going to have to fuss with every time

Lyrra