Outside a couple of books written in the late 1960s and early 1970s by Czech dissidents about the economy of Czechoslovakia, I haven't read any material that specializes in the economics of the Eastern Bloc. Nevertheless, your questions are pretty common to the general study of the Cold War, so I can answer them (though I am personally hoping that someone else will step in who could recommend a book on the topic).

What were their economic relations with the Soviet Union? Was it something similar to European colonialism, where the colonized countries were kept underdeveloped while being exploited for their natural resources?

The situation was in a way the opposite. European powers colonized areas that lacked industrial development but which could supply the ruling nation with natural resources. The Soviet Union, on the other hand, ruled over an empire of nations that more developed than itself (notably Czechoslovakia and East Germany) and which lacked natural resources that the Soviet Union could supply (petroleum products). The Soviet Union, however, could still exploit these economies, as seen below.

Did the USSR have something like The Marshall Plan to help rebuild war-exhausted economies of those states and create effective allies against The West?

Again, it was in a way the opposite situation. After the war, the Soviet Union sought reparations from one of the most industrialized areas that it controlled, East Germany. This meant physically stealing industrial materials from an area already devastated by the war. The Soviet Union further exploited the new economies it ruled over by prohibiting nations in its sphere of influence from participating in the actual Marshall Plan, which both Polish and Czechoslovak leaders had hoped to do. Stalin subsequently oversaw the creation of "Comecon," the Council for Mutual Economic Assistance, which sought to integrate the Eastern Bloc economies while also excluding them from trade with the West. The organization never realized its goal of integrating the economic policies of its member states (i.e., in creating a single five year plan for the entire Bloc), but it did find ways to exploit these economies anyway, notably in a free trade agreement in which all the nations of the Eastern Bloc shared their patents with the other member nations. Again, Czechoslovak and East Germany were far more advanced than the Soviet Union, so the benefit flowed in only one direction--from the more advanced nations to the Soviet Union.

How insistent were the Soviets on implementing soviet economic model in satellite states, things like collectivization of agriculture and central planning?

In the aftermath of the war, during the period of rising tensions with the West, the Soviets were absolutely insistent on the member states adopting the "Soviet model" for their economies, which included all the things you named, although the transition was not as rough for these nations as it had been for the Soviets in the 1920s. In the aftermath of the Hungarian rebellion of 1956, the Soviets compromised by allowing the Hungarian Communist leader Kadar to pursue a "Hungarian road to socialism," but this proved to be little different from the Soviet model as Kadar, over the years, fell in line and became quite loyal to the Soviet central leadership. More interestingly, in my opinion (i.e., I'm about to talk about my own area of research), the Soviet leadership under Leonid Brezhnev supported a Czechoslovak initiative in 1968 to reorganize its economy to include certain profit motives after Czechoslovakia suffered a horrible recession in the mid-1960s (the Czechoslovaks had been one of the richest peoples on earth prior to the Second World War, and so, in short, a lagging Czechoslovak economy threatened Soviet interests in several ways). The reform movement, however, simultaneously challenged the Soviet model throughout the Eastern Bloc and allowed a free press to question Communism altogether, and so the Soviet Union invaded to put a stop to these changes. Oddly enough, the Soviet Union itself would try to implement similar economic and social reforms twenty years later during the "Perestroika" period shortly before it collapsed.