At the moment, all visitors are required to self-isolate
for 14 days when they arrive to Ireland from another country.
As this is under constant review and changes, the section of the HSE page on Travel
is the one you want to keep an eye on.
It also gives you more details regarding the self-isolation requirement and form.
Regarding the overnight stay in the UK, I would suggest you have a look at the government website.
They have a section with information regarding travelling to the UK
as the requirements are different there.