What are the differences between a personal relationship with God in his Church and an individualistic relationship with God?

I use the analogy of thick, rich chocolate syrup in milk, when I talk about the Holy Spirit.  He is there in us all.  He has settled down in the bottom of the glass.  We have to stir Him up to be able to taste Him in our lives.  When I help others in any way, when I feel the gratitude of God's help during the day, I can feel the Spirit in my emotions.

Jesus came here to form a community.  This is the only criteria I give to RCIA candidates.  Yes, it is important to know the doctrines and learn the prayers and rituals.  The most important thing to come out of the classes is, when they run into issues in their lives, I tell them, if you remember to go to Jesus for help and feel His friendship and the trust that He will be there for them, I have done my job.

The individualistic relationship is the trap our Protestant brothers and sisters have fallen into.  Some of them say once "you have a relationship with Christ", you don't need the Church.   

What does it mean to “have a personal relationship with Jesus Christ”?

The expression can mean a great deal, very little, or nothing at all. Some people speak of having a personal relationship with the Lord in such a way as to suggest that Jesus could be one’s “buddy”; blasphemy or presumption are involved when one reduces the sovereign Lord to the level of the manipulable.
On the other hand, Saint Paul indicates that through baptism a believer is incorporated into Christ, with a real union resulting (CCC 1267–70). The initial relationship is then nourished through prayer, the Scriptures, and the sacraments, especially the Eucharist.

A relationship with Christ, then, is essential for every Christian. The only caution is that the transcendence of God (His absolute otherness) be kept in view as one enjoys the benefits of His immanence (His nearness revealed in Christ).
Questions to test for balance are: Do I feel as though I am known and loved by Christ as an individual? Do I hear His challenge to grow into His image more and more, leaving sin behind?

Stravinskas, P. M. J. (1996). The Catholic Church and the Bible (Revised Edition, pp. 117–118). San Francisco: Ignatius Press.

The insight into Christ dwelling in every other person enables one to express charity toward others with greater spontaneity. Instead of seeing only someone’s personality, race, nationality, gender, status, or characteristics (which you like or do not like), you see what is deepest—one’s union or potential union with Christ. You also perceive everyone’s desperate need of help. The transcendent potential of most people is still waiting to be realized, and this awakens a great sense of compassion. This Christ-centered love takes us out of ourselves and brings our newly found sense of independence into relationships that are not based on dependency, as many relationships tend to be, but that are based on Christ as their center. It enables one to work for others with great liberty of spirit because one is no longer seeking one’s own ego-centered goals but responding to reality as it is.

Keating, T. (2009). The Daily Reader for Contemplative Living: Excerpts from the Works of Father Thomas Keating, O.C.S.O., Sacred Scripture, and Other Spiritual Writings. (S. S. Iachetta, Ed.) (p. 15). New York; London; New Delhi; Sydney: Bloomsbury.