My grandfather brewed in old butter churns with wet towels over the top. You should be fine burping your bucket. You will eventually graduate to using glass carboys and blowoff tubes. But for now, what you have will work.
It will not blow the top off because once it builds pressure up it will start to open and the pressure will seep out and it will regulate before the top blows off. Most tops on plastic buckets are not air tight anyway.
You brew is bubbling now so fermentation has started. It will form foam on top in the next 48 hours.
Relax....this is supposed to be fun!
