It is not difficult for Irish citizens to get a Chinese visa from Hong Kong.
You don't need to book accommodation before travelling to Hong Kong and China, the hotel booking is generally not required for visa application, however, April is the busy season of hotel for Canton Trade Fair, you'd better book the hotel in advance, otherwise, it is very very hard for you to find a hotel in Guangzhou.

If you have previous entries to Mainland China, it is possible for you to apply for multiple entry visa from Hong Kong.

You won't be refused entry to Hong Kong as an Irish citizen who enjoy 90 days visa free access to Hong Kong.