Hi, and no problem about asking any questions, that how we learn , here are my answers:
1 - That message you can simple dismiss and you can continue to upload the latest firmware onto your board. Its just a warning that 3DR have added to the new mission planner versions as there has been an increase in people selling face pixhawk boards (as official 3DR pixhawk). Since the hardware is all open source its no problem to make clone boards, but you just cant pretend they are made by 3DR. So this is why the message has been added.
2- You cant edit the measured current value directly, but rather the amperes per volt value. More details on how to do that is shown in this video:
3- That does sound strange, and it could be an issue with the bluetooth driver on your computer. Some other people have had the same issue with bluetooth and found that after the uninstalled the bluetooth drivers and downloaded the newest version for their PC the problem was fixed. Also make sure you are using the latest version of mission planner.
Hope that helps, if you have any other questions please let me know.