Just to weigh in on the whole SMT/Persona thing:
Persona 3 & 4 are very different to the mainline games and all other spinoffs, to the point where I would rather consider those two games an entirely separate thing. The only similarities are that they are turn based games that share demon designs.
I would only recommend Persona 3 FES to someone who hasn't played any Atlus RPG's before. I tried to play it after playing some others and I just had to give up because I really didn't enjoy what I was playing. P3P fixes up the gameplay a lot I hear, so I might give it another chance through that. As it is, Persona 3 is the only Atlus game I've ever played that I actively dislike.
Persona 4 fixes up the many gameplay problems I had with P3, while sadly inheriting the pacing issues and bad dungeons. It is much easier than Nocturne or Strange Journey, so isn't a bad starting point even if I feel it is worse than those games. On the flipside, Persona 4 has a cast of really enjoyable characters. If the whole slice of life anime highschool thing appeals to you then go for it.
If you don't want the slice of life stuff but still want a way in to the mainline games that is slightly easier I would look into Digital Devil Saga. They are pretty great games with some of Meguro's best music, but they lack the demon fusion system that is pretty much an SMT standard.
I personally think there are no problems just jumping straight into Nocturne, but some people disagree. It is harder, but seriously not that bad initially. You'll get some time to learn the mechanics before the game stops taking it easy on you. Just make sure you fuse a lot and use buffs. You'll need them.