The scanner recognises when you have a Post-It on the sheet and then stops: but this can also be switched off: an ultrasonic sensor checks at any time whether two pages are randomly fed at once - that's why the Post-It is recognised as the second page.
As for the 200 gr paper: I think it depends on the bendability of the paper: a cardboard box will probably cause a jam... The sheet of paper goes through the scanner in a straight line, but at the end it has to be "bent" back to the front. You would have to try it!
With postcards (I don't have anything heavier/thicker to test) it works perfectly!
The scanner is very good and fast: please note that the indicated speed was measured at 300 dpi: at 600 dpi, scanning is somewhat slower.
All in all, a good, useful and fast scanner: recommendation!

I have scanned a wide variety of documents (including heavy glossy brochures) without any problems. However, when processing stacks, the feeder is sensitive to sheets that are not exactly the same size or that slide differently (e.g. cut open brochures or originally folded documents). In this case, turning the stack and scanning "upside down" often helps.

I haven't tried it out yet. We only use paper up to max. 100g/m2. From the size of the feeder (especially the gap width for paper thickness), this should work well.