There are different variations of the marine rush. As the barracks are completed you should have the resources to pump out marines. What to get There are many worthwhile upgrades that you may wish to invest in. The first upgrade you should get is stimpacks. These are great for both offense and defense.
Stimmed marines shoot twice as fast and can move much faster as well.
The range upgrade is also worth while, especially if you are using bunkers. If you are making wraiths you WILL want to get the cloak upgrade at the control tower, otherwise wraiths are pretty useless. Tanks NEED siege mode, otherwise they are basically useless. Spidermines are also a valuable investment, research these if you want to mine strategic locations with vultures. If you get a science facility and science vessels, research irradiate to use against the zerg and emp to use against the protoss.