Thank you! You are absolutely right: the bare HC-05 is a 3V3 board. The eval board commonly sold on eBay/Amazon/other hobby sites already comes with the voltage converter on it. Hence, you should be able to plug the board straight into the 5V and it will work fine.
Thank you! I exported the coordinates to this website: https://www.darrinward.com/lat-long/ You'll have to manually separate the logged data to the format that matches theirs. You could write a simple script in Excel.Alternatively, there might be a CSV to KML converter somewhere that will allow the logged data to be displayed on Google Earth.
Looking at the product page, the Feather uses a Bluetooth LE module which would be incompatible with most ELM327 modules.The ELM327 adapters on Ebay are all at around £5 (about USD$7). Don't go for shields, because they are indeed super expensive. Go for the individual components, as they are cheaper.