I think, traditionally, the only parts you ‘have’ to say is the Our Fathers, Hail Mary’s, and Glory Be’s.
Although for some ways of praying the Rosary, these aren’t even mandatory in the traditional decades structure. Consider, for instance, the Rosary of the 7 Sorrows of Mary. There are at least two ways I’ve heard of for saying that one, and neither includes decades. One is to say 7 Hail Mary’s between each Sorrow (each of which includes 10 Bible verses) and another is to say one Hail Mary after each verse or two or three verses, coming out to the same number of Hail Mary’s. As there are 7 Sorrows and 7 Hail Mary’s for each, it comes out to 49 Hail Mary’s (unless there are more at the beginning and end- I think this may well be true. I’ve only said this Rosary once).
I sometimes say the prayer to St. Michael instead of the Oh My Jesus, for example. If you wanted to add a prayer to the rosary, the places to do it are between decades (after one Glory Be and before the next Our Father), before the Rosary, after the Creed, or after the whole Rosary is said. That’s what was taught to me at least.
Some people add different things to the Hail Mary to emphasize the Mysteries, but I dont’ particularly like changing the Hail Mary. For example, they’ll say, for the first Joyful, “Hail Mary, Full of Grace, the Lord is with thee, blessed art thou amongst women, and blessed is the fruit of thy womb, Jesus (announced by St. Gabriel to be in your womb). Holy Mary…”
Well, whatever appeals to you
. I add words within the Hail Mary’s at times, and I always add something at the end of each Hail Mary. After saying, “pray for us sinners, now and at the hour of our death,” I often go on to make specific prayer requests about
what I would like her to pray with me for (not excluding anything else she wants to pray). I also pray the Hail Mary’s very slowly, a lot of the time, line by line, pausing, meditating and sometimes praying over (or repeating) each line. This makes it take a long time to pray the Rosary, but it gives a TON more depth to me than did my first recitation of a decade.
I recited the first decade pretty quickly the first time I ever recited the Rosary, and the words swiftly began to fly by me without my paying full attention to them. Then I started adding prayers at the end of each Hail Mary and going
really slowly through each Hail Mary, and they blossomed for me. They have become a wonderful blessing, through that.
Also, I sometimes add (or repeat) personal words within the Hail Mary’s. It makes the experience richer for me. For instance, if I’m saying a decade, I might say:
Hail Mary, Full of Grace . . . Full of Grace . . . Full of Grace, the Lord is with thee. Blessed art thou among women, and blessed is the fruit of thy womb, Jesus, my Great King, my God, who was sacrificed for me. Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Pray for me that I might be fully united to the Sacred Heart of Jesus through your Immaculate Heart. Pray that I might be consumed in love and in the graces that stream from you through Christ our Lord, and that I might become those graces to everyone around me. Amen.
Often in the ending part of the Hail Mary, I’ll focus specifically on the topic of meditation. I’ll usually pray for unity with the Sacred Heart of Jesus, and often for unity with it through the Immaculate Heart of Mary.
It really makes the Rosary richer to me, to do it that way. Though I know it’s astoundingly rich to loads of people who do it without any additions
. This is just what works very beautifully for me
.
The mysteries are emphasized differently during the different liturgical times. Sundays in Lent are reserved for the Sorrowful. Sundays in Advent, the Joyful. I don’t pay attention to which mysteries are for which day, I just pray whichever I feel like, but I make a definite effert to pray the Sorrowful more in Lent, and the Joyful in Advent.
I’m pretty much the same in that. I haven’t yet been Catholic long enough to pray them with emphasis on liturgical seasons, but I pray them pretty much in whatever order I want, except that I try to pray the Sorrowful on Fridays.
I’m sure that it will help you grow closer to Jesus and Mary and help you on your journey. 
I use it so I’m “hands-free” while praying in the car.