I use .028 wall seamless stainless. for 3/16, 1/4, 3/8 I have had good luck with it, For 1/2" it will flat spot on tight bends. If you can find a place local to you to get stainless tubing some will deliver it for a small fee. For the most part you are going to be under 10' for your longest run.... I don't like putting in unions if I can avoid it. if you need to, relocate an adjustable proportioning valve to under the car. once you set it.... it is pretty much left alone. I have used aluminum and stainless fittings on the stainless line. if you are an all out race car pushing the limits of brake pressure you may want to do it all in stainless.
some will argue that aluminum fittings will stretch over time. considering a stock vehicle may use a brass Tee or brass ends on a steel line. I think for street cars the aluminum is a viable option. I will say that an aluminum fitting can round off just as fast as a brass one. the stainless... not so much.
for cutting I use a rigid hand cutter. and deburr the ends. I also take the time to file them flat. yes file. I have found if you miss anything on the deburring and try to flare the tube, you end up with a sort of Galling mark.
for the actual flaring I use what is called a Roloflare. I think it was an aircraft tool originally. mine does 3/16 to 3/4. in a 37 degree flare. it is a hand tool and will give you a workout.
this is like the one I use but a different brand.
https://www.aircraftspruce.com/catal...ringtools2.php
keep it oiled nice on the threads and the tip.
I have used the hydraulic tool and find that it is cumbersome and gets heavy after being all over the car. and if you have a line in a tight spot, it is almost impossible.
another tip..... I absolutely hate uncoiling tubing. buy straight sticks if you can.
use your scrap pieces to have generic bends. place them where you need and make your bends on the long pieces. tape them to the care and measure between them.
If you mess up..... fix it. you now have a template for what you need. They are brakes or fuel nitrous or fire suppression. A simple $30 line and 2 tube nuts and 2 sleeve could be the cause of a failure.
last, take your time to map it out on the car, painters tape... pinstripe tape. a marker. if you have the factory lines they may show you a route to follow.