RSI ( Repetitive Strain Injury ) is the disease I believe and as long as you take short breaks ever hour or so, You should be fine and that is if you don't play other games that require you to click in any other ways or tap keys rapidly and osu would be one of those examples as another game as that's where most people get there RSI from if they play it to long.
You can't donate for kits anymore. The OP kits cost 25,000 coins now, I'll update this tutorial soon.
More than a year has passed from when I posted this, good times (This doesn't count as bumping old posts as this is just a tutorial, right?)