The difference is the difference between metaphysics and epistemology. One can consistently accept that there is no first cause (everything has a cauase), small

The difference is the difference between metaphysics and epistemology. One can consistently accept that there is no first cause (everything has a cauase), smallest thing (everything has a part) as examples while rejecting infinitely chained justificationa or vice versa. They don't necessarily or usuallydepend on eachother.