First of all, welcome home to Rome. Hope your RCIA goes well.
And before picking a saint, sit back a bit and see what a saint is. Saint is believed to be a person of virtue who was in full communion with God, and from that communion, emerged the very person that God designed when the soul was created. With this in mind, look for a saint with the same type of spirituality (if theyāre down to earth, or more of the mystical-type), their theology (if you base your faith on your feelings of love and conciliate them with God, or if you base them on reason, for isntance) and how they lived their lives.
Letās take me as an example. My name is a Portuguese translation of Peter (Pedro), so my patron saint, by default, is the Apostle Peter. I felt that every aspect of Peter as described in the Gospel was lived by myself in different ways when I converted (āGet away from me Lord, for I am a sinful manā, and I was trying to keep my spiritual high alive as Peter did during the Transfiguration, and I even refused the offer of having my feet washed during the Holy Week), and he easily entailed with me, especially when I felt the need of going out and showing others the wonders of the faith in Jesus.
But, St. Peter isnāt alone, as I have a patron saint per se, which I knew after Peter, but it was amazing how much in common weāve had theology-wide, and that is St. Thomas Aquinas. We both stood for natural theology (based on reason, to put it short), and his way of thinking about Christ and conciliating Aristotelian philosphy and science (Iām a science type of guy) was so similar to mine, that I started theorizing that they gave me his brain when I was a baby (not trying to call myself as great as Thomas was, but I think you get my point

). We were so similar, that I bought a medal of him which I bring everywhere I go. One key difference I had from him was the force of will to counter lust. But since I have this medal, heās helped me in keeping myself in control (with no real reasonable way of explaining how, but it simply works!). I chose him because he was the expression of who I was turning out to be as a Christian, and I may even feel that I have a vocation to join the Dominicans like he did, they just seem a fit for what I want to do for life!
About the vocation, donāt rush about just yet, and but keep your vocational discernment open to any possibility (if you want some quick help about this, watch
this and
this). You may be in a spiritual high right now and feeling thatās the way to go, but you may not even pass the postulate phase. Just slow down!
If you think that the Franciscan spirituality and theology is similar to yours, you might want to look at the saints of the Order. For instance, the saint of the people (heās non-official, but everybody loves him because he was born here) in Lisbon is St. Anthony of Lisbon and Padua. He was an awesome preacher, was really inspiring to many people and even made St. Francis consider on his thoughts on people that were theological scholars like Anthony grew to be, being a canon regular before being a Franciscan. Iād seriously recommend him, his most famous miracle and a legend that everyone learns at school is his preaching to the fish in order to attract the peopleās attention. I love him and I ask him to pray for me before I go to Mass, and I think you could too!
Good luck choosing a patron saint, and may he bless you and pray for you. I will be praying for you as well for a good RCIA. Welcome home!