When I personally raised Mottled Javas I felt that they had a weaker immune system compared to other breeds I've raised. They caught coccidiosis, I had one with failure to thrive and potentially Mareks and multiple seemingly healthy ones drop dead

My line may have been inbred so I can't speak for the whole breed. I would definitely be pretty cautious about making sure the bedding is dry and clean just because they may be more susceptible to illness where most chicks would be fine. On a better note, mine had awesome temperaments! Very personable and gentle. Super sweet chickens who were quite intelligent! They're also quite an old breed that was the ancestor to Plymouth Rocks but sadly fell out of popularity. I wish you luck!! Don't feel intimidated just after raising them once, if I were to do it again I would be a bit more meticulous and keep an eye out for any signs of illness

Keep in mind my experience doesn't sum up the breed, just wanted to throw it out there!