Will the Union State of Russia and Belarus ever be fully realized and if so, will a new "Russian Empire" arise with interest Ukraine and the Commonwealth of Independent States?

No, not unless US loses the Cold War 2.0[1], which is highly unlikely. While Lukashenko is in power, he will be opposing such takeover  because in the united state his role would be to bring coffees. That is the reason he criticized annexation of Crimea - he read the writing on the wall that he was next. However, Russia's chances to maidan Lukashenko are zero - they tried it in Donetsk, you saw the results. When he is gone, his successor will be maidaned by pro-EU forces - hopefully something good comes out of that. [1]

Even a Russia-Belarus union seems unlikely. Belarus' Lukashenko has http://www.themoscowtimes.com/news/article/belarus-says-russias-annexation-of-crimea-sets-a-bad-precedent/496633.html, notably, and hasn't yet recognized Abkhazia and South Ossetia as separate from Georgia. Even though in many respects Belarus http://belarusdigest.com/story/why-belarus-not-ukraine-16368--especially in being large Russophone and eastern oriented--there's still http://belarusdigest.com/story/will-belarus-last-long-17549 to make the prospect of absorption into a greater Russian state unpopular. (To say nothing of the interest of Belarus' leadership in continuing to run an independent state, not an autonomous republic never mind a collection of provinces.) Kazakhstan is even less likely to accept absorption into a Russian empire. To a hugely greater extent than Belarus, Kazakhstan's government since independence has actively sought to re-Russify, boosting the status of the Kazakh language, encouraging the immigration of ethnic Kazakhs from neighbouring countries while doing little to stop Russophone emigration, and trying to develop Kazakhstan's profile internationally through building ties with China and other countries. Kazakhstan may well be cooperating with Russia as it serves Kazakhstanis' interests, but submersion into a greater Russia is even less likely. The countries that are associating with Russia--Belarus and Kazakhstan being the most notable, but Armenia, Kyrgyzstan, and Tajikistan being more recenbt additions--are doing so because a Russian alliance serves their interests. (For the last three countries particularly, the fate of their immigrants in Russia matters hugely, while Armenia is of course concerned with Azerbaijan.) If it stopped serving their interests, they would stop.