Either or....
Tom Morris' bell cranks come with braided already finished off at the bell crank so I don't change them. If the plane is a ".35 size", or smaller and I have to make up the lead outs, I will often use solids. I like .032 on anything using a .20 and up. Have used larger on .60 size stunters. A dear friend/brother was once using ,025 solid LOs on his "big" planes. Had one failure at a very inopportune time and stopped that practice then and there.
Windy used to sell .032 solids long enough to use in his "big" stunters so the stuff is out there.....
As to mixing up the lines, I always color code the "wrapping" on the wingtip terminals. Red for UP. When I first make up a set of lines, each line gets one red wrapped terminal. After a while, I swap the lines end for end and still have a red line end terminal for up to match the UP lead out. After Aaron once hooked his brand new Ares backwards, out came the Radio Shack red wrapping wire. When I am thinking of it, I use the green on the down. Red shrink wrap is becoming my choice for covering the end terminations on the UP line (gotta keep up with "modern technology"! LOL!!).
Big Bear