Sal gave you the info needed for the extensions, they also come with gold plated ends. Bigger is better!! The reason for the gold is it isn't supposed to tarnish. Standard ends should be removed every year and cleaned, I used the spray electrical cleaner and plugged them in and out. Being because I'm me and very lazy I didn't clean mine every year and sometimes I ended up with sluggish servos or servos not working at all. My giant scale planes were just too much work to maintain. That's why today I buy bulk wire and lengthen my servo leads by soldering on the wire length I need. Just pure lazy is all.
When you get all your lucky soldering stuff you need just ask and I will do A photo show for you. When at Harbor freight pick up one of those cool little extra hand things with all the gator clips to hold stuff, it's easy but I won't do it until you are ready!!
That Lazy thing again. That and I have A bunch of stuff going on in my shop right now.