Basically i’m asking if I need to buy a micro SD/USB adapter to format the micro SD on my PC (Windows) or if can can count on the Raspberry to connect on its own to my network (WiFi or Eth) and make the microSD card available to my connected PC...
The Pi3B+ is bootable from USB– MilliwaysApr 9, 2018 at 0:49
It's possible but it would be much easier just to get an adapter which are really cheap (probably £1 off eBay).
The possible way to do this is to remove the card from the Raspberry PI, setup network booting (this is not trivial but there are lots of tutorials around including on raspberrypi.org) and then insert the card once the PI has booted. The PI itself can then be used to format the card.
Of course you need a bootable Raspbian to setup network boot. Apr 7, 2018 at 11:47
Ideally maybe but you certainly don't need it. I used the downloaded Raspbian image and extracted the files directly from that using kpartx although there are other ways as well. Apr 7, 2018 at 15:17