I am coming late to this thread but I thought I would throw in my 2 cents since I have relevant experience. I have been using an LX100 in an Ikelite housing for the past three years and I have been very satisfied. I was initially attracted to the LX100 for its M43 sensor, awesome Leica lens, 4K video capability and ability to manual white balance.
I also considered the RX100 Mk 3 but was put off by its inability to MWB without a filter and overheating issues (note that these issues have been addressed in later models). The LX10 was not out at the time but in retrospect, I still would have purchased the LX100 due to the larger sensor and faster lens.
I went with an Ikelite housing for reasons of cost and I have found it to be just fine for my needs as an amateur. I am sure that the ergonomics of the Nauticam are far superior but it is in a much higher price range. This is compounded by a complex and expensive three-port system, which seems to defeat the simplicity and utility of a point and shoot.
For lights, I have a pair of Scubalamp V4K Pros for portraits and two BigBlue ALX2600 for macro. I like the Scubalamps but I regret that I did not spring for the V6Ks at the time. The BigBlues are serviceable for macro but are very cold and are only 80 CRI. I will eventually upgrade both.
Over time, I have added on a WD-4 wet lens for shooting wide as well as a CMC-1, two UCL165-M67s and a custom flip holder for macro. I mainly use the CMC-1 but I do stack all three lenses for very tiny stuff. I also made a DIY quadropod using ball arms for improved macro stability.
The main limitation of the LX100 is macro due to the comparatively low magnification ratio of the lens. Since this has become a primary interest for me, I am currently upgrading to a mirrorless setup that will leverage the Olympus 60mm macro.
You can see some of my footage on my YouTube channel which is linked in my signature block. Happy to take any specific questions on my setup if it is helpful.