Thanks to vestureofblood there is a great tutorial here in the blf. Although I wouldn’t leave the part as long as he did on the frying pan, since you actually saw the mcpcb getting a little brown. But I guess it was just for the tutorial. You also can do it with normal solder but then I’d recommend to first cover the contacts of the star as well as the contacts of the led with some solder. That’s how I always did it. I don’t think it makes sense to buy solder paste for just a few leds. And you also don’t need to reflow the rest, you can just solder them on with a soldering iron.
Regarding the firmware - there is a tutorial here in the budge…. 
OK, I guess you can also just buy a pre-flashed one. If you give me your address I could also send you one although I couldn’t promise that it would arrive in time for the competition.