When adding sims to an existing game with intricate backstories like this couple and presumably other sims, the decision of whether to play out the backstory or not first doesn't have to be all or nothing. I usually play out just enough of it to establish a baseline and a bunch of sim relationships (bad ones from their former lives included, in this case) to have a solid foundation to work from. In other words, I would probably begin this storyline just before these two sims ever met but not so long before that I get lost in the pre-story details and never get them together to where they were meant to be.
I suppose the same would apply for new games if I ever actually started any new games meant to be kept going long-term rather than adding characters to my existing one, but the idea is the same either way.
I don't have a hard and fast rule about skills and career levels when developing new characters. I mean, I love working my sims through the various skills and career ladders, I'm very patient and to me that kind of slow progression is a crucial part of gameplay. But you can't have a presumably YA or Adult sim who is essentially starting their life over not have had some skills and experiences behind them. These sims at least need to have Level 5 or 6 on Painting and some musical instruments respectively to start out or the backstory doesn't make as much sense. Probably some Charisma, Logic, and Athletic but still mid-range and not all the way over the top, for the former Criminal history.
I think Romeo and Julio (yes, I am sure that's not their real names) should both be in the Political career, the very beginning stages, or perhaps one giving Law Enforcement a try in their new world, and thus be on "opposite sides" of something or other until they actually meet and get to know each other. That's where the fun part of the storyline would begin for me. :)
