Riva:
The camera is a Oly EPL3 and a Oly PT-EP05L which has front LED lighting powered by 2 AAA batteries. This lighting is pretty useless and I dont use it so the space can be used by my project.
Is this LED needed for auto focus while submerged?
IRremote library has been ported to/hacked for the ATtiny85 see TKJ Electronics » ATtinyRemote and Porting the Arduino IRremote library to the ATtiny4313 | ubiyubix so all the goals might be possible using IR (assuming it works underwater okay).
IRremote is useless for the E-PL3, since it doesn't have an IR shutter release. Olympus put IR shutter releases in its DSLRs (E-5 being the current DSLR), but not its PEN and OM-D series of cameras.
Well the shutter release is fairly simple, but whether there is room in the case for the shutter release may be a problem. Olympus doesn't list a shutter release as an accessory for the PT-EP05L case, so there may not be an opening. I had a similar problem with my original steampunk camera, where I put my E-P2 in a 1915 Kodak Pony Premo 5x7 body. Given the size of the Kodak, there was no space to put the RM-UC1 (Olympus wired shutter release). So I suspect you will have the same issue with the PT-EP05L. In that case, the only real alternative is to craft a servo that sits on top of the shutter and presses the shutter. I assume you need to put it on top of the PT-EP50L, which means you need to make a waterproof container to hold the arduino, radio, power, and servo. It sounds difficult.
Now, it may be you might have enough wiggle room if you take a cheap clone wired shutter release (to get the Olympus plug), and splice the wire and immediate have bend to get to an area where you have more room. Note, I've had at least two shutter release cables break when I made 90 degree kinks in the cable, so you will need to be very careful.