Don't buy a TV for its Smart features. They're not very good. Handy for Netflix, YouTube (especially for small kids) and RTE Player but you could get same features and more with Chomecast as you say. A couple of years down the line your Smart TV won't run the latest versions required whereas a Chromecast can just be replaced.
Saying all that, nearly all decent TVs come with Smart TV and only the very basic models don't have this and they are also substandard in other ways (picture, sound and build quality). So think of it as paying €150-€200 more for a better TV - with the added bonus of Smart TV. If you do spend that you can make do with the inbuilt Smart features for now and only buy the Chromecast later, when the TVs smart features look outdated but the TV itself is still going strong.
Samsung TVs have the best smart features and I think they're very good for other reasons too, so I've one of those but, as I say don't be too swayed by the Smart features.
As an aside its shocking how poor Smart TV technology is compared to, say, mobile phone technology. Have a read of this which sums up my feelings perfectly: [broken link removed]