Hello I`m starting a yukon and was wanting to know aprox how much cedar I`ll need.

According to the experts (not me) you will need (the total surface area of the kayak) divided by (the exposed width of the strip). If you are using 3/4" wide strips and a rolling bevel the exposed width of the strip is 3/4". If you are using 3/4" wide strips bead and cove the exposed width is 5/8". The result of that calculation will give you the number of feet of strips you need. I'd figure about surface area of about 60 sq ft for a single kayak.

All I can find here is 1x12x8 wouldn`t it be better to find longer.

Many of the builders on the forum say they even prefer to work with 8 ft stock. You cannot escape at least some joining. The longer the original boards the more room you will need to mill the lumber. i.e. to rip 8 ft lumber you need straight line room of at least 16 ft plus the depth of your saw. For 12 ft lumber that jumps to 24 ft plus . . .

its cold as heck here so time I get shop warm time to go to bed

As I hear it, it's cold as heck all over the country. My garage was 22 degrees when I started working today and 37 degrees when I stopped. That was with two heaters going. For milling lumber it just depends on how much cold you can put up with. When you start stripping you'll need to warm the shop up to satisfy the glue's requirement.

As for scarfing style, you can find other builders who cut it along the thickness, others who do it along the width, and still others who just do butt joints. I'd expect you'll hear from some of each.

Relax. Enjoy the building process. You're not over your head. Later on, you may have to say that over and over to convince yourself ;^], but you'll probably do just fine.