The tanita scale is one of those scales with the electrodes that touch your feet. They are pretty accurate, but they are best for monitoring relative bf than absolute. They are around .5% accurate within themselves, so I would recomend testing yourself 3x a week or so (at most, most people recommend once a week) at around the same time, morning is the best.
22 is fine, a teensy bit high for an athlete. Men I think they want 12-22 or 15-25 or something I forget. A fighter in good condition should be like 8-12 I would assume. Extra bodyfat won't affect your heart unless you have a ton of it, it is mostly just extra weight that has to be moved around and that is what burns you out faster.
For the underwater weighing I would recommend going to your local college as if they have a Movement Science or Exercise Physiology department I bet they have it. No telling how much it will cost though. I think it would be a waste unless you really need to know withing 2-3%