There are lots of brake lines and lots of choices.
First off that "3 way joint" is actually not any sort of valve at all, its the brake light switch. You can continue to use it, but not with that brake line you're looking at. If you want to use the brake line you're looking at with your stock master cylinder then you are going to lose your front brake light switch.
So you can do one of several things. One is you can buy another master cylinder (MC), one that has a brake light switch built into it. If you are going to do that you might as well decide now if you want dual disks or not, and if so when you go looking for a new MC get one with either a 5/8" or 16mm bore. The size will be indicated somewhere on the MC body.
Your other choice is to get a shorter braided line, one to go from the MC to the stock brake switch and then run a second braided line from it to your caliper. At the caliper you have three choices in how to attach it. You can buy a line similar to the stock one with the correct fitting on its end. You can buy a line with a banjo on both ends and attach it to the switch on one end and directly to the caliper on the other - even though the caliper was never designed for this attachment many folks get away with it. The third option is to put a universal fitting (10mmx1.25 to AN-3) in the caliper, a universal banjo at the brake switch end of a universal hose. If you go this second route you simply duplicate the line for the second brake and use an extended banjo bolt at the stock brake switch. The last method allows you to add the second brake later, with no loss of existing parts.
That help any?