You may use the same primer for both classic PCR and Real time PCR. However, I prefer the primer covering the shorter region of cDNA while performing the Real time PCR.

Yes you can use

Not always.

if you optimize the deisgn and efficiency of the primers for qPCR then you can also use them for normal PCR. Not all normal PCR primers work efficiently for qPCR. even if you purchase published qPCR primers always run your own standard curve to verify efficiency - I've used some that were NOT good

http://www.bio-rad.com/en-us/applications-technologies/qpcr-assay-design-optimization?ID=LUSO7RIVK