All of this varies from seminary to seminary and diocese to diocese. Most of the time, if you have student debt you will be allowed to defer it until your studies are complete. In my case, I had student loans, and got them deferred, and when my studies are finished and I am receiving a salary as a priest, I can pay them off as anyone else normally would. Most of the time, your diocese will cover the cost of your tuition. Some dioceses pay for college seminary, some do not. Nearly all will pay for Theological studies after college seminary. These are questions you need to refer to your pastor and your diocesan vocations director.