This article says nothing about the Holy hour on Thursday (ideally) meditating on the Agony in the Garden and only mentions confession in passing. I’m not sure that’s right to leave that out.
The Holy Hour on Thursday evening (or on Friday, when some people do it instead) is an
optional added devotion to the Sacred Heart. It is
not a required part of the First Friday devotion which came from the Vatican-approved private revelations to St. Margaret Mary Alacoque. Jesus simply asked people, via the private revelation to St. Margaret Mary, to receive Holy Communion on nine consecutive First Fridays. At the time of the private revelation, people tended to receive Holy Communion very infrequently, often only once a year to fulfill the precept of the Church, so the point of the devotion was to have people receive Holy Communion more often.
St. Margaret Mary had a separate private revelation where she said Jesus asked people to make holy hours on every Thursday night - not just the one before First Friday. So that became a whole separate devotion. People making the Nine First Fridays are often encouraged to make the Thursday holy hour as well (assuming they have access to a church or chapel for Eucharistic adoration on Thursday) but it’s not a required element of Nine First Fridays.
Confession is
not a required part of the First Friday devotion unless you need to confess in order to get into a state of grace before you receive Holy Communion. If you are already in a state of grace, then you don’t need to confess again just to fulfill the requirements of First Friday.
(I note that for First
Saturday devotion, you do need to confess between 7 days before and 7 days after in order to fulfill the conditions of the devotion, even if you are in a state of grace already from a previous confession.)
Finally, regarding the “yearly Sacred Heart feast”, it wasn’t part of the private revelation of the Nine First Fridays devotion to St. Margaret Mary. The feast was started locally in France by St. John Eudes in 1670. St. Margaret Mary started having her private revelations a few years later and they did not require people to observe the feast (which wasn’t even being celebrated in very many areas at that time). The feast of the Sacred Heart spread along with the devotions promoted to St. Margaret Mary but they didn’t come from the same source.
So what we have is three different devotions to the Sacred Heart here, one of which (the Sacred Heart feast) pre-dated the revelations to St. Margaret Mary. If you want you can do all three, but if you’re just doing Nine First Fridays then you’re not required to do the other two to fulfill the requirements of Nine First Fridays.