you could use... 

yes

Is the question on using same primers for RNA (with RT-step) and for DNA (gene)?.

It can be, but you may get higher band for DNA, if there is an intron in between.

yes you can but some time its bit difficult to amplify the DNA sequence if you have used same primer sequence for first round of amplification (reverse transcription with RNA primers). the length of amplicon will depends upon either you are using cDNA or gDNA as templete for DNA sequence amplification.  it might help you, good luck

Yes

yes