If its just for social media and you don't pixel peep your photos, I think should be fine with just v20. I've been dragging along my MFT cameras for 2 trips and didn't use them at all as most of the photos are instantly uploaded to FB.
Can't comment on the external lens usage.
For manual mode, trust me it's the easiest of all. Just set it to manual, and make sure the AE-L button is not lighted in green. This mode is what the forumers called Manual-Auto (or Auto-Manual I also forgot). Otherwise, you just play around with the ISO and S buttons. Rule of thumb, ISO to be set the lower the better around 50-200. If too dark, play with S button. If S is set too low, the picture will "shake". That's where u can increase S and compensate with ISO increment by a bit. Play around with those, you should master it in no time. Don't be surprised you can take better or more engaging pics than if you use your normal cam.