Just cut off the end bits that castle had pre tinned for you. When they tinned the ends they don't twist the wire strands and that causes them to expand. Just chop them above the tinned area, strip back the insulation, twist the ends with your fingers and then tin them with solder. Be careful not to press too hard with the soldering iron as it will cause all the strands to unravel again. After you do this you should be able to fit them into the bullets relatively easy. Its how I do it and works a treat every time.

As for the bec do like others said unless you are using large scale servos. When using large scale servos I like to run a Y-harness with the big servos so that the receiver doesn't have to carry all the current. This isn't necessary if you are going to just use standard size servos.