Two separate authorisations: the employment permit grants the right to work in a specific job, while the entry visa grants permission to travel to and enter Ireland.
Conflating these two is the most common cause of misjudged start dates. Nationals of visa-required countries need both — permit first, then a visa application through the relevant embassy, which can add weeks or months. Nationals of non-visa-required countries can travel on the permit alone. Map your candidate's nationality against the visa-required list at offer stage, not after the permit arrives.
No — a visa-required national cannot lawfully enter Ireland for work until the visa is granted, even with a valid employment permit in hand. Booking flights before the visa decision is a common and expensive mistake; wait for the visa, then travel.
Ireland maintains a list of visa-required countries; nationals of those countries need an entry visa on top of the employment permit, while non-visa-required nationals can travel on the permit alone. Check your candidate's nationality against the current visa-required list at offer stage — it changes the timeline by weeks or months.
No — they are separate authorisations from separate departments. The permit (from DETE) grants the right to work in the specific job; the entry visa (from Immigration Service Delivery) grants permission to travel to Ireland. Visa-required nationals need both, in that order, and each has its own timeline.