Years ago, when I was in a Catholic college, I acquired enough credit hours in philosophy for a major, but since, back then, you couldn’t have a double major, I ended up majoring in English Lit with two minors; one of them in philosophy.
Given the nature of the college, there was a lot of Aquinas. A lot, but not to the exclusion of all others. I think I ought to give fair warning. Studying Aquinas is a lot like studying Shakespeare. There are a lot of levels to it, and it takes an enormous amount of study before one really “gets it”. Even then, one is very unlikely to exhaust Aquinas in a lifetime, just as one is very unlikely to exhaust Shakespeare. But I will say that one can feel fairly comfortable with Aquinas at the point where he can “think in it”. Until then, it’s just a knowledge accretion.
Aquinas never did claim that the “proofs” really proved God’s existence. He, himself, said they don’t. His purpose was to demonstrate that Christian beliefs are not “unreasonable” according to the most widely regarded philosophical system at the time, which was Aristotelian philosophy. The latter has an internal “logic system” to it; a sort of “thinking mathematics”, and that system is also incorporated into Aquinas’ works. Therefore, before we were ever exposed to Aquinas, we studied (Aristotelian) logic first, then Plato and Aristotle, and only then did we study Aquinas. Understanding Aquinas also requires at least a bowing acquaintence with Plato. Hate to keep piling on, but it’s also helpful to study Augustine in advance as well, because Aquinas cites his works frequently. He cites the Church Fathers a lot too, and even Jewish and Arabic philosophers.
Aquinas’ works are not light reading, and were not intended to be. They were intended to be read by people of at least a minimum level of scholarship. Unfortunately for us moderns, that “minimum level” was a lot higher then than it is now. Unfortunately as well, we can’t understand a lot of other, later works in Western Civilization very well without understanding Aquinas at least somewhat. Our progenitors knew a lot more than we do, I’m afraid.
But I think if a person approaches Aquinas with the idea that it’s a major study, and if one is patient with it, he won’t be dissatisfied with it at all. Ultimately, it does affect the way one thinks. There is a whale of a lot of Aristotle and Aquinas in western thought, and in my opinion, gaining an understanding of them also aids in approaching and understanding our own world.