Yes; there is already a "Union State" between the two and both sides would benefit. Belarus has a much weaker economy than Russia, and the creation of a common currency would be beneficial. Citizenship and freedom of migration between the two countries could also be beneficial, as well as military cooperation.
No; they may already join the Eurasian Economic Union in 2015, which would keep Belarus sovereignty but also improve their economy; the independence of Belarus must be maintained. Taxation will also be an issue, as well as popular support. We also can't risk Russia becoming the superpower it once was, as one annexation may lead to many more.
The two countries are very close and I do not agree with your other answer because its just wrong bro not to mention offensive
History will repeat itself. The soviet union was dissolved some 20+ years ago. We already saw what the soviet union has done with power. A counter power, NATO and the EU will only make another cold war. They might get stupid, because this annexation of territory is like Hitlers anschluss. They will keep wanting more, and more. Except Germany won't be there to help them invade Poland.