A6000, what else do I need to start?

If you're shooting stills, red filters are absolutely unnecessary - they just steal your light, and shooting RAW then using spot white balance in post-processing is a much better way of restoring colors. Video is a more thorny issue, but even there, MWB is generally a better option.

Regarding housings, I really don't see much point in Fantasea FA6000 when SeaFrogs Salted Line has pretty much all the same features at half the cost or less.

For strobes, your main options are Inon S-2000 or Sea & Sea YS-01 for entry level, and Inon Z-330 or Sea & Sea YS-D2 for advanced. The new Retra flashes should also be available in a few months if you're willing to wait, although it's a fairly safe bet that initial production will go towards filling preorders.

For lenses, your main options are:

1. 16-50mm f/3.5-5.6 kit lens - the zoom range is useful for a wide variety of subjects, but on its own it's neither wide enough for the big stuff, nor capable of macro. You can put it behind a flat port with 67mm threads and augment it with wet wide lenses for wide-angle and wet diopters for macro, similar to how fixed-lens compact cameras are used underwater. You can also shoot it behind a dome, but then you forgo the option of wet lenses.
2. 10-18mm f/4 lens - ultrawide, useful for reefs, wrecks, medium sized or larger subjects that let you get in close. Requires a dome port, 6" or larger - flat ports produce extremely strong pincushion distortion at shorter focal lengths. Not useful for small stuff, or shy subjects such as sharks that won't approach you.
3. 16mm f/2.8 with VCL-ECF1 fisheye converter - the only native option for a fisheye, which gives you a wider field of view than even the 10-18mm lens, but at the expense of significant distortion. The wide field of view is useful for getting close to larger subjects such as whale sharks, manta rays, giant groupers, etc, as well as reefscapes or wrecks, but lighting such wide-angle shots is a significant challenge, lack of zoom is limiting, and fisheye distortion can spoil some shots.
4. 30mm f/3.5 macro - cheap, good quality, can do 1:1 macro (i.e. life-sized subject on the sensor; can fill the frame with a 24x18mm subject) but short focal length makes for a very short working distance - in order to shoot these small subjects you need to pretty much bump the lens into them, and the more mobile critters will not tolerate that and swim away. Lighting at such close ranges is also a problem, as the port will shadow your lights or strobes. Can also be used for intermediate size fish portraits and such.
5. 50mm f/2.8 macro - good intermediate focal length, but reportedly has trouble focusing behind port glass.
6. 90mm f/2.8 macro - excellent image quality, great for macro and supermacro, reasonably fast and accurate autofocus, good working distance on the small stuff, but heavy, expensive, eats lots of battery power (I can reliably get three dives out of a battery with 10-18mm, but only two with 90mm), and larger subjects require staying way, way back - outside of strobe range, and way too far away if water clarity is less than optimal.

Strongly consider getting a vacuum system if the housing that you pick supports one. The way it works is, some time before a dive (I usually do it overnight, the previous evening) you use a pump to evacuate air out of the housing, and then a sensor monitors the pressure inside. If any of the seals aren't air-tight, air will leak in and an indicator will start flashing, alerting you to the fact that taking the housing in this state underwater isn't safe.

Kind of stating the obvious here, but underwater photography is a challenging pursuit, and safely handling a camera underwater - particularly if it's a large rig with a dome port and strobes or lights - requires very good buoyancy skills drilled into muscle memory. You have to be able to hover inches off the sea floor without touching it, maneuver in close confines, and do it while concentrating on other things (namely, the subject(s) and the camera). Keep in mind that these camera rigs are quite draggy, and moving one through the water will have a noticeable effect on your air consumption.