By same charge I mean that same nature of charge i.e " Both positive or Both negative " . To be more specific consider two plates both of the plates are held face to face close to each other much like a capacitor but unlike a capacitor they both have positive charge so will there be a potential difference between them >?
If by magnitude difference you mean Plate A has a charge of +1 and plate B has a charge of +9, then there will be a potential difference. If by magnitude difference you mean Plate A has a charge of +1 and plate B has a charge of +1, then there won't be a potential difference.
Yes. If you have two positively charged plates of different charge magnitudes and fire a stream of electrons between them, the electrons will deflect toward the "more positive" plate. Though really the electron stream isn't exactly necessary, since the two plates will repel each other indicating a potential difference right off the bat.