I've been waxing my bikini line for ages and it's made the hair so much finer and lighter, that I find it's worth it. Also, after years of doing it, the pain has become very mild. I used to go to a professional but a few years ago I started doing it myself with microwavable wax. I find it really convenient, but it does take a few times to get the technique down, so I would go to a pro for the first few times. At home I don't heat the wax up as hot as my cosmetician used to heat it, but I prefer it this way.
If I have the patience to do my legs, I wax 'em, but most of the time I'll just attack 'em with an Epilady or some equivalent. Similar to waxing without the mess of the wax. A bit more painful, but faster and cleaner, so it's a trade off....
As for needing hair to be of a certain length for waxing/tweezing, yes, it needs to be about 4-5mm for it to be effective. But, waxing does cause new growth to be thinner than shaving (shaving cuts the hair at the thickest part, while waxing pulls it out from the root. New growth comes in tapered thinner.). I don't let myself be bothered by a few mm of growth and no one's ever said anything to me in a class. I decide not to be bothered by it.
All of that said - I agree with tacha666 -- never change a running system before a big event / competition! Experiment when you know you have the week to live with possible unwanted side effects/results.