So when you say 2-3 times year, does that mean on water? Because an open cell foil is going to fill up with water if you crash it. They do make water relaunchable foils, but those start getting pricey and I personally would rather just use an Inflatable.
To answer your question on the benefit of 2 vs. 4 line kites, hmm, i guesss this is kind of hard to explain online, but heres my best explanation.

A two line kite(for a foil) has two lines leading to the bridal system.

For a four line, they have two that go to the front and two that go to the back, and the two that go to your front go to the center of your bar. These then run through the bar and down into a your harness. The back lines on a four line go to the outside of the bar. What happens that is different is now the bar can move in and out and when you do this it changes the angle of attack on the kite. This is because the front lines stay the same lenght and the back lines shorten or lengthen when this happens. So with this sheetability, if you pull it towards you then you get more power, and if you let it out then it will be not quite as powerful. This can help greatly in gusts especially.
If you are looking for a 2 line foil kite, go with the slingshot B-series problably 6 or 8 meter or the Ozone Samuri but im not sure what sizes they have.
For a 4 line foil I kite I would go with the Ozone Frenzy, and again im not sure what the sizes they are.
If your are going to go with an inflatable kite that can also be used during summer, there are tons and tons of good kites out there. Personally I like slingshot the best for my kites, and for you I would maybe try to find a used Slinshot GTO or Deisel. These are nice lower aspect easy flying kites that would work perfect for you. But like I said, there are lots and lots of other good companies that make good lower-moderate aspect kites that you would like a lot.