Shark photo???
Duh never mind, looked over it
It's a stunning shot!
I had my diving licenses for a while and would have loved to take my camera with me but never dared.

Talking about waterproof what do you think of this shot taken underwater link

The WR lenses have a SP coating so they should be easier to clean and when you use a hood there would be much that could get on it.

What do you mean with that Mike?

I don't see an lot of difference between the beta and the non beta

DA*50-135 or Tamron 28-75 f/2.8 for portrait work with your stobist kit

A lot can happen in a your, I would stick with your K-M.
camera bodies will only get cheaper while lenses get more expensive

Mike that's like searching a needle in a haystack...

For P-TTL flashes this one is better link
For best value you will most likely will come out at the Metz48

If you want to do cheap strobist work then something like this is the cheapest you can get.
Triggers: Cactus v4 (transmitter, 2x receiver)
Flashes: 2x Yongnuo YN460-II
Here is something about light stands link
For umbrella, since you said group shots I would go for 2x 60" convertible white-bounce/shoot-through umbrellas.

All in all it would be around the £300

it really depends on how far you're from the stage which lens would be better, if you get a 70-200 you will have some occasions that you didn't find it wide enough at 70mm and the same is true with the other lenses on the long end that it isn't long enough.

They are all very good lenses so you can't make a mistake there.

Too be honest I don't think flash is the way to go with his harsh light or you are thinking of multiple flash set-up maybe?

The theatre have some power stage lighting I would suggest using those and get a DA*50-135 with his f/2.8 it should be able to cope pretty well with the light

You're using multiple flash with wireless triggers if so could it be that one flash is out of sync.
So one flash flashes to early capturing the shutter and with the second flash that does work al right making the shutter grey instead of black.

They needed to change the sensor in the K7 to make it suitable for video so with just a firmware upgrade you wouldn't come far.

it stays there till Bob opens up, although I just read some messages that the PM system might not be working...