Tyranid Army Building - Advice Required

I have been building up my Hive Fleet Leviathan army over the last year or so but I've not really put a great deal of thought into which models to buy. Originally I just started off with a handful of random purchases and I was then able to buy a second hand Assault Brood set. Since that time I haven't really bought much for the Tyranids as I wanted to get to a point where I felt my Necrons were "finished".

Now that the new Tyranid codex is about to be launched, along with a host of new models, I think its nearly time to put the Necrons back to slumber in their Tomb World and for my version of Hive Fleet Leviathan to take to the gaming tables. I currently have a limited budget (probably about £200 max, ideally a bit less) to spend on some new models so I'd appreciate any advice from anyone as to what else I should consider buying. It should be noted that I know very little about Tyranids as I've only ever played a couple of games against them so I really am a bit clueless at the moment as to where to go next, the models I currently own are as follows:

• Flying Hive Tyrant
• Hive Tyrant (unbuilt)
• Tervigon
• Trygon (unbuilt)
• Carnifex (unbuilt)
• Carnifex with Deverourers
• Carnifex with Talons
• 24 Genestealers
• 32 Hormagaunts
• 9 Warriors
• 8 Rippers
• 32 Termagants
• 10 Gargoyles

Hive Fleet Leviathan - Flying Hive Tyrant

I've been working on this particular model (on and off) for many months now I'm really happy to have finally finished it. The Hive Fleet is starting to take shape now and with the new models due to be released soon, and more importantly with permission from the wife to buy quite a lot, I'm hoping to have my new Tyranid army up and running before the end of January (with the slow rate I which I paint these models it will probably be a very long time before I have a fully painted army though :-( )