Hi there! Welcome to the forum!
So, to the list:
HQ - Ethereal = 2 Markerlights
Hmmmm...generally I prefer an Ethereal in a Devilfish cruising around with Firewarriors over standing in a crowd waiting to get pummeled. He does have some pretty useful abilities for resisting damage (Sense of Stone, the Price of Failure, etc.), but his offensive abilities are much better (Storm of Fire, Zephyr's Grace) and work best when operating at short range. In a long-range static list, I think a Cadre Fireblade is maybe the better choice. You'll get better mileage out of your foot FWs and a Target Locked Markerlight to boot that uses a much better BS than those two drones. The Fireblade also works out to ~15 points cheaper than the Ethereal + Drones and is more likely to survive a sniper's bullet.
Troops 2 x 10 Fire Warriors
If these guys are on foot, buy them each a Shas'ui (or, if you're buying the Cadre, buy a Shas'ui for just one of them). The Ld Bump is nice. Even with an Ethereal, the worst thing that you get assaulted and get yourself challenged, sticking you with the choice between 'the Ethereal Dies and gives up a VP' or 'no leadership powers'. Bummer.
I suppose if you run with *just* an Ethereal, the Ld bubble will work most of the time. As said, though, I think static formations aren't the Ethereal's strong suit. If possible, increase each squad to maximum size.
Elites 3 x Crisis, each with 1 flamer, 1 x twin-linked fusion blasters
In a 750 point game, the number of targets that will need a good fusion blastering is fairly limited. I would recommend TL Missile Pods over this set up, as they rock at killing transports (of which you will likely see several) and have a good long range that will compliment your static plan. Also (and very importantly) the triple flamers + Supporting Fire make them an *excellent* assault deterrent for your firebase.
Fast Attack 2 x Piranha, each with blacksun filters, gun drones and fusion blasters
Love these guys. Make sure they are each in their own unit and make sure to disembark the drones early. They don't need the blacksun filter for any reason I can think of, so save yourself a few points. These guys need and want no upgrades apart from the fusion blasters. Expect them to die.
Heavy 2 x Hammerhead, each with blacksun, railgun and twin-linked smart missile
Pretty solid. If you didn't buy submunition rounds for each, do so--they are invaluable. That said, I would suggest you seriously consider buying a Skyray instead of the second Hammerhead. The markerlights are really useful, all those Seeker Missile can hurt if launched at the same target, and (as mentioned above) you just won't need a whole lot of anti AV13/14 firepower at this point level. One Hammerhead with markerlight support and two Fusion Piranhas should do it.
That's my .02. In a small game like this, playing static means putting as many shots at long range as possible and being able to account for transports and fast units trying to close. The number of truly hard targets you'll need to cull is limited to the occasional terminator squad, and they drop just fine to concentrated pulse fire with markerlight support. Oh, the other reason to take that Skyray: there is the outside chance you'll be faced with a flying monstrous creature or other flyer, and then you'll *need* the skyfire to stay alive.