Dont feel bad, your willing to learn and also - It may not be your fault the first one died, the black and white should not have looked like that from the pairing, could be a genetic anomaly. If your temps can be relied on cutting should not be an issue.
Regarding the incubator being home made, that should make no difference. - if temps are stable and your using a thermostat and its well insulated and your thermometers are calibrated for accuracy and temps are relatively even in all areas…
Regarding making sure thermometers are accurate, Private Message (PM) me (I think they call it Dm here) , i have made so many posts about how to do that and cant be bothered again, unless that is you ask me specifically
Check this thread for tips on any incubator temperature’s stability :-
In addition consider drafts on part of the incubator if not well insulated…