47 is an excellent number.
Even 147 would be good, but what is especially important is that this number is consistent.
If it jumps around from 47, to 120, to 24, to 231, to 75... this is going to be a problem and other people will see you 'warping' back and forth. Having a consistent 400 is better than the example I gave there.
UDP and TCP are two different networking protocols. It would take too long and be too hard to explain what this means, but in a nutshell UDP is faster, more efficient, and uses less overhead than TCP. Compare this to baseball: Right fielder throws ball to first baseman. The drawback is there is no error-checking built into this, which means that the right fielder can't see the first baseman, and vice versa... so someone could stop the ball half way and substitute it for a different ball (or even throw it away altogether) and neither player would be any more wiser.
TCP on the other hand is slower, less efficient, and uses a LOT more overhead. Same baseball example, except the right fielder has to first show the ball to an umpire who then has to call the first baseman to let him know the ball is on the way. Then the ball gets thrown. Then another umpire examines the ball to make sure it's the same ball... then he hands the ball to the first baseman... and then he calls the right fielder to let him know that they got the ball intact. If something is wrong, then the first baseman has to ask for the right fielder to throw it again.
Because of this, UDP can't handle any packet loss at all, and if any of this is detected it switches over to TCP which can tolerate a bit more abuse... the drawback is lag (due to having to resend lost packets), 'rubber bullets', and anything that is 'time sensitive', such as aiming for the right wing of an enemy... becomes much more difficult. People usually don't get to fly with TCP for very long, as if their connection is too poor to support UDP.. then it's probably not going to support TCP either.
Basically, when you get that message.. it means land your perked ride because likely you only have a few seconds before you get disconnected altogether. I have gotten lucky in the past though... lost UDP during FSO but finishing out the night on TCP... Luckily the networks out here are stable enough to where this isn't often an issue.