I do a 120 page magazine and when I make the pdf for the web (lo-res) the file size is only 4 or 5 mb.
I don't know who in their right mind would send you a 120 page document with all their styles and text in tact? I'm not sure what advantage having someone else's styles would be to you? As there is no naming-convention for InDesign styles, style names are made up by the individual indesign user and would be totally different from one person to another; along with that all the styles would have different fonts, sizes, leading, space before and after, justification and a plethora of other formats???
I'm not sure what your goal is with your request? Sounds like you have an issue proofreading things sent to you?
I work with an external editor and this is the workflow we have:
Author sends in text in word files
Editor rejigs authors work in word files
Layout is made in InDesign
Editor reviews layout from PDF and makes final adjustment with comments/queries made in Acrobat
Author sees article with any queries from editor and addresses those
Changes and queries made in InDesign
All changes checked in-house with 4-eye review
When product is ready it's editor revises the entire product ensuring all changes are implemented.
Hope that helps.