Flyrants do a lot better in the air then they do in the ground. Being forced to wait a turn between switching flying modes and assaulting is a death sentence. Nearly all Tyranid players will use a Flyrant with two sets of Twin Linked Devourers and an Electroshock Grub template. This is what internet folk mean when they use the term 'Flyrant' because it's just that popular and just that good that any inferior builds are the ones that need to be specified.
Now, the Tyrant kit doesn't have Devs, so if you already built your beasty, don't worry about it. Just make sure your opponent knows what your list is before a game.
Warriors are a pain. Include them because you have nothing else, but really think about dropping them when you get the chance. Good choice in keeping them cheap. I'd add Deathspitters to the ones without a Strangler, just for that extra strength in then shooting. But don't invest any more into Warriors. I've found that if an army can kill the three you have, they'll kill five or even nine just as easily. If they can't even kill five, they won't be able to kill the three you currently have.
More Termagants. If you're gonna take them, take truckloads. Cheap is good, but if you ever feel they should perform, one in three can be upgraded to a Devouerer. That way the ones that will die, because many will die, stay cheap and the Devs stay safe. So in a brood of thirty Termagants, you get ten with Devs. I still take Termagants despite building Nidzilla. I like the tarpitting they can do.
Gargoyles are like Termagants. Take truckloads or don't take any. Atleast twenty per brood.
Which means, you're right on track with the next things you want to buy. Add in something with more killing potential though when you have what's on your list. Normally another Flyrant. Maybe an Exocrine or pair of Carnifex. Something that is a legitimate threat to enemy armor. But it's a good start. I think you have a good idea of what direction you're going in.