If you compete in the gi, you have to wear a solid color (no mixing tops and bottoms.) Most competitions only allow white, blue, and black gis. However, if it's a tournament that is fairly traditional they will only allow white and blue gis.
People's asses probably come out due to pant drawstrings coming undone, happens to me at least once a night :P
Compete at whatever belt level you are currently ranked, it does not matter if you are destroying people, usually you want something like this because you win a lot and these dominant wins get you recognition for a possible rank up

Showing you have more competent skills than people ranked the same as you shouldn't be viewed as a bad thing or sandbagging, if it is a problem they would just bump your rank up and depending how you look at that is a good or bad thing :P
In most gi divisions in white and even blue belt there are not many options for leg locks. As a matter of fact I see more DQ's from leglocks than wins in these divisions. In white belt, most tourneys only allow a straight ankle lock and if you turn the wrong way, even if the other guy forced the turn it's a DQ a lot of the time. I do not recommend playing leglocks unless you happen to extremely like the ankle lock or have an opening for it. I don't know if blue belt opens up any more options, have to look into it. I think you can't really play many leg locks until purple, then it opens up in brown and black.
My advice for tournaments would be learn a couple of good grip breaks and learn some gi grips yourself and use them to your advantage, even if you view them as cheap. I started strictly no-gi and I viewed the leverage a gi gives you almost as a cheat code coming from no-gi lol. Combine the famous 10th planet system of overhooks and underhooks with the gi! Your used to having badass over/underhooks already, now grab some material on top of that! If you overhook someones arm you can grab your own collar or their collar to maximize leverage on their arm. Since you both have sandpaper on its very hard for them to get out of even an overhook done this way. If you have butterfly guard do that with your overhook and with the underhook grab the back of their belt. You can really take your time if you get dominant gripping. And my last piece of advice is if someone is going for a collar choke from guard/mount, if they have 1 arm in your collar you are fine, the 2nd arm is the one to worry about that can finish the choke. Sometimes they can sneak the 2nd arm in somehow if you give too much attention to the 1st arm.