After you put concealer over blemishes, do you need to put anything else on top of that to finish it off?

Nope, just reapply later if necessary.

no you dont. you can use a compaq powder. but you dont have to

usually when i know where i need to put my concealer on i put it on before my foundation. then i add my poweder

Naw, you don't. Some people need to use pressed powder to 'set' it. Or to hide shininess, but I don't do that myself.

Cheers