The science achievements are easy, you should end up with 25 points in each tree by the end of the campaign if you do all the missions, especially the 4 protoss missions.

The armory achievements are harder, you won't have enough to get them all in one playthrough. However, if you can save up a million credits and never buy any upgrades until the end of the game, then save, you can just spend it all to get one achievement then reload the save and buy everything for another achievement. That's what I did, and on normal difficulty you should be able to get through the campaign with that much money to spare.