I am not sure where to post this.
I am thinking of one or more denominations or being non-denominational. Where do I convert?
I am thinking along the lines of: Seventh-day Adventist; Catholic; Jesuit; Methodist; Anglican.
Can one follow all of these at the same time? Which denomination is best? Is it best to follow just one of these? Still a beginner...
Ah, now that this has been moved to a more open location I can reply.
Jesuits are a religious order of Catholics with a rigorous dozen year training. So you are then left practically with Seventh Day Adventists, Catholics, Methodists, and Anglicans. But you might want to consider even other groups mostly depending on what is available in your area.
Almost every town in Great Britain will have an Anglican church. Larger towns will have a Catholic church and might have a Methodist church. The Seventh Day Adventists will be less common.
There are more Catholics at church on a given weekend than Anglicans at church even though the Anglicans are the established church. I don't know how many Methodists or SDA are in church in Great Britain on a given weekend.
Many of the Anglican churches started out as Catholic churches more than 500 years ago when Henry VIII appropriated then to be Anglican. Those are all of the beautiful Gothic buildings. Catholic churches are much newer as the Catholic churches had to be built after the Catholic Church was finally again legal in Great Britain.
What you want to pay attention to is doctrine of the group and local congregation as well as the vitality of the local congregation. Anglicans are in turmoil and are shrinking in so many places. But some local congregations may be thriving. Anglicans are divided into different groups, the liberal, the evangelical, and the Anglo-Catholic. And they are losing members. If you go Anglican you should figure out to join the group you agree with first. Some will be in communion with the archbishop of Canterbury and some won't. Some will be woke and some will be conservative. The nearest congregation might or might not be for you.
The Methodists are also in turmoil over homosexual ministers at least in the USA and are undergoing a painful split. In the USA they are losing members rapidly. If you go Methodist figure out what side of any split you are on first and then look for an agreeable congregation. Again the nearest congregation might or might not be for you.
Catholics are in some turmoil as well. Maybe not as earthshaking as the previous two, but it pays to check out the congregation. Again the nearest congregation might or might not be for you. I'm Catholic. I'll tell you how I find a Catholic church that suits me when I'm traveling. You can use this yourself to advantage. I check masstimes.org and enter in my location. I then search for parishes that have adoration in addition to just mass times. I find those parishes to be more prayerful and more active. of those I check their web sites and then I go. I don't know where you live in Great Britain but just tooling around I found a place I would consider visiting if I was ever in Manchester. It's St. Alphonsus parish, Ayers Road, Old Trafford. It has mass every day except Monday and adoration in the daytime every day. It's hard to tell too much more from their website. Another place, in London this time, would be Tyburn Church on the north side of Hyde Park. It's the site of the King's Gallows.
There is another Catholic option if you find you would like to be Catholic but you also like the older Anglican style of worship. That would be the Walsingham Ordinariate. Whether or not this of interest to you I might recommend a visit to Walsingham, East Anglia. There is also the Oratory in London that is very worth a visit.
As far as the Seventh Day Adventists go, they are really very different than Anglicans and Methodists and Catholics. They have some very distinctive doctrines, most obviously that they think you have to worship on Saturday and not Sunday. They think Catholics will eventually force them to worship on Sunday and then the world will end. They ARE Christian, but can be hostile to people who don't worship on Saturday. I have no idea about any turmoil they may be experiencing.
How do you become a Christian? You pray and you study and you consult with others and you get baptized when you are ready. You should take adequate time to be sure you know what you are getting into. Some Anglican and some Catholic congregations will offer a program called Alpha as a nice way to explore Christianity. Or another program called Sycamore. Oh, get a Bible if you don't yet have one. I recommend a translation called the ESV, as it is modern and accurate. There you can learn about the guy who climbed a sycamore tree just to see Jesus. I also recommend the Catechism of the Catholic Church. Both the ESV Bible and the CCC can be bought at almost any bookstore or on-line. Once you get going on your reading, and after an Alpha or Sycamore program, look to join a class that will actually prepare you for baptism. It's a slower process of learning and testing the waters and finally committing, if you are ready, to change your life and to live for Jesus. I like to say Alpha is fine, but it really needs a Beta and a Gamma, and a Delta. The baptism class would be the next step but then it's life-long learning until we all get to Omega some day.
You probably have a bunch of other questions. So ask them. Try putting in your postal code to masstimes.org and see what pops up.