Lead-free is fine.

Lead-free with poor quality flux is abhorrent to use.

Get good quality lead-free with good flux from a reputable manufacturer (Kester is good, as you mentioned) and it's fine.

In fact, I prefer how thin and quick to wet out SAC305 is over the lower melting point of Sn63Pb37.

I have made quite a few keyboards (including handwired) and a few other electronics projects with lead-free solder and it has never been an issue. I use lead-free solder with a resin core, set the iron to the recommended temperature, and make sure to tin the tip.