The trouble with low cost carriers is that they treat each flight separately. So say you fly with EasyJet from Belfast to Liverpool to Barcelona, you would have to book your Belfast/Liverpool and Liverpool/Barcelona flights separately. And even if you allow plenty of time and the first flight arrives in to Liverpool late and you miss your flight to Barcelona, tough luck, the airline washes their hands of responsibility even though you used the same airline for both flights. That is the risk of travelling with low cost airlines, I suppose.
As for Moscow, you are far better off, flying with a proper carrier e.g. Air France via CDG or BA via LHR, good deals can be found if you are flexible and willing to look for them. And if your first flight is delayed, they have to sort you out on another flight as another poster already mentioned.
Apparently the best way to see Russia is to do the Trans-Siberian Express from Moscow-Mongolia-Bejing. You would need to allow a minimum of three weeks to do this to get the full benefit out of it. You can do the whole trip in 10 days non-stop.