A lesson a fortnight is ok. It just takes longer. Some will say that 2 week intervals is too long and you should increase the frequency (I was lucky and started with 2 lessons a week, but I still lost momentum over a bad winter), but if you haven't got the time/money what can you do? Start as you have planned to and if it isn't working change it. My only advice is do it sooner rather than later - You'll get a far better start by flying bi-weekly over the summer than by waiting until winter when the weather gets bad again and cancels lesson after lesson after lesson...