Okay, I don't play marines, so take the advice with that in mind.
But I understand that you are mainly facing NidZilla
Dev squads, should do very well against the devilfexes. why pay for termie honors? Why get a plasma gun? I would assume they would do fine on your side of the board. You don't want them to get close to the enemy.
Tac squad: Why a plasma pistol? Do you really want to be within 12"? 24" means you are in devourer range, and that is bad. Skip the term honors, and the plasma pistol. Get a lascannon. (Either instead of, or in addition to the lasgun)
Landspeeders are your friend. They have range and speed, two things Zilla doesn't have. But I don't see the role of the typhoon, I think you are better off with a tornado.
Vindicator: Again with the 24" range? Any devilfex or deviltyrant can take one out on the side armor. I would go with 2 predator annihilators, and one whirlwind
I might play with the idea of getting some razorbacks. 90pts for a twin linked lascannon... not bad. Just keep them out of LoS of the sniperfex, and out of range of the devourers.
Tactics:
Set up to give yourself good lanes of fire. Cover isn't important, since Nids don't have anything worth using cover. Now, blocking line of site is different, and is still useful. But a devil flyrant shooting you in cover, and in the open, does the same damage.
First 2 turns. All lascannons that can, take out the flyrant. It is his only fast unit.
All Missle launchers take out the devilfexes. They are his main offense.
Any missle launchers that don't have a shot at a devilfex, target the small units. Stealers or gaunts or whatever.
Any lascannons that can't hit the flyrant, target either another HT, or a sniperfex. Note: It should be the one that will be easiest to take out. ie. a sniperfex that is in LoS of a lot of lascannons. Don't waste a shot on something you can't kill next turn. (unless that is literally all you have.)
Leave the Zoans for later. A HT with guard will take forever to kill.
If a devilfex has only 1 wound left, then use a tac squad to finish it off. No sense using 4 missles to do that job.
Speeders: keep them out of devourer range. That means you may not be able to use the assault cannons for the first couple of turns. Keep them out of LoS of the sniperfexes if you can.
If the flyrant gets too far away from the rest of the TMC's, then you can get close to the flyrant, and blast it with 12 HB and 16 AC shots. Kill it dead. (But again, *not* if it will mean the death of the landspeeders.)
Remember, the assault cannon has a range of 24". The devilfexes can move 6", then shoot 18". you really don't want them taking out the landspeeders. So only use the assault cannons if you can hit one thing, and not get smacked by everything else.
Whirlwind goes after the soft units. Stealers, raveners, gaunts, rippers, etc.
Turn 3+ At this point, You should have killed off a number of units, but they are now within devourer range and have taken some of you out too. My army suggestion has 5-9 lascannons. So the flyrant is hopefully gone, and 1-2 devilfex.
Finish killing those off. At this point, you can be more daring with the landspeeders. If the sniperfexes are staying behind in cover, you can zoom off and hit them and stay safe. With the missle launchers, and landspeeders, you may be able to take out the rest of the devourer shooting.
Kill the devilfexes first. Then missles go to soft targets, landspeeders go to flyrants and fexes.
Eventually, even your commander can join the fight and kill of some stuff... maybe.
I don't know, my description sure makes it seem easy, and I know it isn't this easy. But hey, it might be.
Remember, the goal for the first two turns is to lose no models, play it safe and just shoot the heck out of him. Make him use cover, it will slow him down. Yeah, he has 2-3 sniperfexes.... big deal. Flyrants and devilfexes are top priority
edit: Hmmm... after reading Striogi's... it may be a good idea to switch from missles to lascannons. OTOH, if you go with the predators you may not need 21 lascannons....
Voice of Reason: I had the same question, but to take dev as elite, you need to also take infiltrate or tank hunter.
And there are 4 landspeeders, but his points are off.