Timothy welcome to the best place on the internet.
As for the first purchase, I say it depends on what you can afford.
But get the best one for the money you have available, it will last a long time,and won't depreciate much like other types of clothes.
If your a chap who may in your opinion put on a little weight in the next few years I suggest buying the next size up and moving the straps to fit now.
Since I was your age I have managed to put on only a couple of inches so bear this in mind.A kilt is a investment, and treated right will last all your life.
Best wishes.