If you start ML with the default ML team you will automatically be in PII at the start of the season and the first division league where you promote will be the one where your club comes originally. So if, for example, you start a game using the ML team with Barcelona, you will start at the PII League which has promotion to Liga BBVA. If you start with the club lineup of Barcelona, you will be at Liga BBVA which has relegation to PII League.
Be careful, though, if you plan on jumping from league to league. Only one division 2 exists in the game so... I think you know what I mean. Just for fun, I started a game with a Portuguese team and at the end of the first season I was relegated to PII League. The thing is, I received some offers from clubs from other leagues, so I decided to move to Ligue 1. Here's the catch, at the start of the second season, I checked the competition info for PII League -- it was to be expected, but for my surprise there were 3 portuguese teams there. I haven't played this second season yet, but my guess is that if I choose to begin a third season on, say, the English League, there will be 3 portuguese and 3 french teams on PII, while on the Portuguese and french leagues, each one of them will have 3 fictional clubs. Ultimately, suppose that on the fourth season I decide to return to the Portuguese League and stay there for more than one year. At first it will feature 3 fictional clubs, but on the fifth season the Portuguese League may well feature 12 portuguese clubs, 2 english clubs, a french club and a fictional club.
(I'll possibly update this post when I finish my second ML season.)