If you want to make things easier for yourself, get a short belly spey line like the Rio Windcutter or Scientific Anglers Mastery Short Head Spey.
However, I would say that you should probably start with a double taper line to better understand the mechanics of the spey cast.
I started with double taper lines and later moved onto the spey lines. I used short head spey lines at first, but found these very limiting. They also have the other disadvantage, they are as thick as rope and don't lend themselves to delicate presentation.
If you are looking to fish the KAC water with the rod, I think that a double taper may be your best bet anyway. These offer more flexibility on smaller rivers. If you get the casting nailed with a double taper then the longer bellied spey lines would be a good progression.
If you are struggling to get double taper lines, a certain shop in Penrith sells a range of their own called Deluxe lines for £15.95 each. I can't say the name of the shop because they are not a sponsor, but I'm sure you know who I mean. I bought a DT9 line from them last year, to try on an old rod. It was every bit as good as lines three times the price. I also buy their lines in various sizes to splice into spey lines and have had no problems with them so far.
Hope this helps,
Good luck with the casting.