Hi Temas,
thank you

I used the 30 macro with an INON UCL165 wet macro lens (+6) for the pigmy seahorse and other tiny subjects...
The 30 macro is more simpler to use, and not only for macro, but also for fish portraits.... some of the pictures to cuttlefish are made with the 30 mm macro.
The 60 mm macro Olympus is FANTASTIC for super macro and very tiny subjects .
The 60mm macro is still usable with the INON wet lens (+6) , but it is very hard to use with Nauticam CMC (+16) or similar wet lens.... surely it all depends by my scarce technics... because I know a lot of friends that are able to use the 60mm macro with the Nauticam SMC or CMC without problems....
So if you ask me which lens buy, I answer you BOTH... because both are perfect for macro .... the 30mm macro is simpler to use... but the 60mm macro is fundamental for tiny subjects, and with the 60mm macro you can stay at more distance from the subject... and this is good if the subject is shy.....
With the 30mm macro, instead, you have to stay closer to the subject....
About the battery of the Gx8 it last for two dives, but for the third dive you had better to change it, because at the end of the third dive you risk to remain without power.... (obviously shooting a lot....)
About the flash , I use this (look at the image) internal flash DMW-FL70-K , it is the flash of the Panasonic Lx100, and it fits perfectly into the Nauticam housing.... connecting the external INON strobes with fiber optics cables....
Usually I set the internal flash in manual mode (not TTL) (look into the FLASH MENU) , and slow down the power at 1/20 , so the internal battery of the Gx8 last more time....
If you want more info, I am here

Scipionems