Is it ok to pray different prayers in conjunction to one another?

Yes, it is OK to combine different prayers, and even encouraged.

Two examples leap to mind:

1. The Rosary

   The Rosary combines the Hail Mary, the Our Father, the Glory Be, and the Hail Holy Queen.

   After finishing each decade, some say the following prayer requested by the Blessed Virgin Mary at Fatima: O my Jesus, forgive us our sins, save us from the fires of hell; lead all souls to Heaven, especially those who have most need of your mercy.)

2. The Devotion to the Drops of Blood / Holy Wounds

   Devotion to the Drops of Blood Lost by our Lord Jesus Christ on His Way to Calvary

   St. Elizabeth, Queen of Hungary, with St. Matilda and St. Bridget, wishing to know something of the Passion of Jesus Christ, offered fervent and special prayers. upon which Our Lord revealed to them:

   To all the faithful who shall recite for 3 years, each day, 2 Our Fathers, 2 Hail Marys and 2 Glory Bes in honor of the drops of Blood I lost, I will concede the following 5 graces:

   1st: The plenary indulgence and remittance of your sins. 2nd: You will be free from the pains of Purgatory. 3rd: If you should die before completing the said 3 years, for you it will be the same as if you had completed them. 4th: It will be upon your death the same as if you had shed all your blood for the Holy Faith.
   5th: I will descend from Heaven to take your soul and that of your relatives, until the fourth generation.

   Blessed by His Holiness Pope Leo XIII in Rome, April 5, 1890.

A distinction needs to be made between liturgical prayer and popular devotion.

Liturgical prayer means that prayer that the Church prays as a body. As the Catechism of the Catholic Church (CCC) puts it,

It is the whole community, the Body of Christ united with its Head, that celebrates. “Liturgical services are not private functions but are celebrations of the Church which is ‘the sacrament of unity,’ namely, the holy people united and organized under the authority of the bishops. Therefore, liturgical services pertain to the whole Body of the Church” (No. 1140, quoting Sacrosanctum concilium 26).

The principal liturgical prayers include the celebration of the seven Sacraments—especially, but not exclusively, the Mass or Divine Liturgy—and the Liturgy of the Hours (sometimes referred to as the Divine Office or Breviary). Also included in this category are the various rites that accompany blessings and other sacramentals.

Liturgical prayer is regulated to differing degrees, and any variation and combination of these prayers is regulated by liturgical books. It is generally not permitted to make adaptations that are not explicitly permitted in liturgical norms.

In particular, it is permitted to combine portions of the Liturgy of the Hours with the Mass. However, it is generally not permitted to add popular devotions to these liturgical acts—for example, praying the Rosary publicly during Mass. See the General Instruction of the Liturgy of the Hours.

Popular devotion, on the other hand, refers to practically all the other prayers that are typically associated with Catholic piety: the Rosary, the Chaplet of Divine Mercy, May crownings, the Way of the Cross, and so forth.

Since they are non-Liturgical, the faithful have complete freedom to pray these prayers as they wish (provided it helps them to be in union with God, of course):

Popular devotions of the Christian people are to be highly commended, provided they accord with the laws and norms of the Church (Sacrosanctum concilium 13).

Since there is, in fact, very little legislation regarding popular devotions, they may be combined, altered, and adapted according to each individual’s and group’s needs.

Hence, if someone would rather pray four decades of the Rosary, or six, instead of five; or if he prefers to say sets of nine Hail Mary’s instead of ten, he is free to do so. He is also perfectly free to combine prayers as suits his needs (provided it makes sense, of course).

Moreover, if he would like to adapt liturgical prayers to non-Liturgical use (e.g., the readings or prayers at Mass, portions of the Liturgy of the Hours) and combine them with other private devotions, he may do so freely.

For an excellent overview of the difference between liturgical prayer and private devotion, see “Popular Devotional Practices: Basic Questions And Answers” from the USCCB.

Insofar as the Catholic Church is concerned on this matter: there is no problem with praying different prayers in conjunction to one another. I personally know many religious (Benedictine monks mainly) who do this very style of prayer daily.

Do not have any reservations about this style of prayer. Go ahead and pray the way the Lord inspires you...