Juan, you are right in 1)
Vulcan is supposed to be orbiting 40 Eridani A (16ī5 light-years), not Epsilon Eridani (10ī5 L.Ys).
Epsilon Eridani is a younger star, smaller but more massive than the Sun. Itīs system is very alike to the primitive Solar System.
40 Eridani A and Epsilon Eridani are located in the constellation Eridanus, a place that has showed some promise for astrobiologists. Gene Roddenberry knew it was promising because the first SETI attemps in 1960 searched these two stars at Eridanus. So he choose the older of the Sun-like stars, 40 Eridani A because an older star is more likely to have Earth-like planets with life on them.
Both systems are very promising suns with Jupiter-like planets. Itīs possible that both stars have rocky planets with water and perhaps life. But 40 Eridani A is an older star. Since life needs some time to develop, itīs the most promising star.
2) It is generally thought that giant Jupiter-like planets at some distance of the habitable zone could help to make life easier in the hypothetical inner rocky planets because they stabilize the orbits and can shield the smaller planets from asteroids. And could have some promising moons even outside the habitable zone, like our Europa (Jupiterīs moon that has oceans of liquid water under its surface and could have life)
P.S: Excuse my English, Iīm not very fluent.