First of all welcome to Tyranids. This army is fun and challenging. HQ is nasty, our Flyrants are the Tyranids heavy lifters. They currently do almost all the damage in most of my games, and I love the dirty buggers. Fleshborer Hives finally have a purpose too.. I would drop Toxin Sacs and find another 10 points for Old Adversary instead, as it acts as a "mini" poison but it benefits those pesky 1's all around instead (you only really lose out on MC with T6+.) Seeing as your guns are twin-linked this doesn't benefit, but to wound most infantry is 2+. It also helps in assault as "scything talons" to hit and "mini poison" to wound it is an excellent addition. Also the 6" bubble is devastating with Hive Guard/Devilgants/Devilfex etc, as they all benefit as well. This upgrade makes our Flyrant ALMOST as deadly as any non Swarmy assault Tyrant.
Hive Guard, as stated above can be nasty combo with Old Ad, and on their own are hands down the best light armour killers we have. So cost efficient I almost always include a full squad as well.
Venomthrope.. So, bad.. (though I love the model so I have a couple paperweights.) For 5 more bananas you just bought yourself another Hormie squad, and for cheaper you get a termagant one. Now these are actually generally more survivable than 1 Thrope, and don't hand over First Blood all the time. If you are wanting to keep him, I'd look into a Prime somehow, at least he helps the floating tentacles, when buddied up. WOULD be great if it just gave shrouded. Too expensive, fragile and the lynchpin to your tactics, so when removed the opponent just laughs and watches everything crumble.. Just play with the right amount of terrain and 5+ is easy to get.
I cut all my Hormagants talons off way back in 5th (foresight maybe?) and made them my Devilgants, although I can fully appreciate a full squad with Toxin. I'm not going to tell you to take Termies, it's all a matter of taste here, I just prefer a bolt pistol to rerolling 1's. (not even including Tervi schenanigans.
Warriors are actually one of my 6th edition favourite home objective holders. (When I'm not throwing my Tervi twins in.) Throw a Barbed Strangler in there for dirt cheap and your babysitters now play at long range (for Nids.) I bought lashwhips and swords for mine, because not even Bloodthirsters will assault your (insert soft Nid here,) with them nearby. More expensive and I only find useful when enough targets are available, but you will understand when they clear out a squad of Termies/Nobs etc.
Biovores.. Oh how I love these guys, I just haven't been able to get ahold of another 2 and I have an old pewter one. Love them, adding in that large blast on the warriors makes them a good pairing. Great Sniper unit because of barrages as well.
Tyrannofex, well I sure loved this guy for a long time, being blind to all the criticism and lashings he took. Rupture Cannon is pretty bad though in 6th, especially having to pay for it. I prefer Zoey's 100%, they are durable in the only Stormshields our army has (Plasma etc still chews through Tyranno,) and have a HUGE amount of options with psychic powers. These guys are literally the utility tool in our army. Marines and Land Raiders? Codex, Low Ld armies? Telepathy, Buffing units? Biomancy.. They are all seperate too and with 6 rolls you are going to get something useful. Take him with Acid Spray if anything, we have no Torrent anywhere else. You want S10? Zoeys Lance could teach Eldar a thing about Lance weaponry. Also, now that my Elfdars psychic defence is a joke, no more 3d6 rolls against those armies.
Now onto some observations about potential issues. The reason SOO many people take Tervigons is because our Troops are all wearing paper armour. Warriors being an exception, but they love taking krak shots to the face.. Focusing on your Troops early will see them out of the game without much effort. Also, you have a fair mix of killpower, and knowing what other models you have access too would help with further changes, although I try not to tell people to change their lists, it could help give direction. Tyrant gets Biomancy, regen + endurance= 3+ regen... Somewhat expensive, but your warlord will be happy when he gets it.
Hopefully some of this helps.