My first bleg

So, I'm hoping that my efforts have resulted in some small readership here.

In the #APicADay series of posts over the past month I've shared some of my learning experience with photography. It was also a way for me to gauge my interest in going deeper into photography as a hobby. As a result I have decided I am interested in pursuing it further. However, I do not have much experience at this point. So, I have some questions I'd like to have answers to from more experienced photographers.

APS-C vs. Full-Frame sensor: Is this a big deal? I'll just be getting my feet wet with interchangeable lens cameras. Is it worth me spending the extra money for the larger sensor when the smaller sensor can use lenses for either?

Canon, Nikon, Sony: What are your preferences and why? I have heard many people say that it doesn't matter that much. But, there are people with definite preferences, which must exist for some reason.

Mirrorless vs. DSLR: This might be more clear at this time, but getting less clear as time goes on. It seems that currently Sony is the only company putting out a quality mirrorless ILC. But as they become more capable in the future, will I have made the right choice?

Anyway, I'm currently leaning toward a Nikon D7500, though I haven't fully made up my mind. A D500, or D750 would also be nice. I've done more looking at the Nikon models because I have an affinity for their optics expertise from other areas. I am open to having my mind changed though.

I do have two fast dogs, that I'd like to be able to take decent photos of, and my current bridge camera is just not up to the task. I'm also interested in macro photography.

Thanks in advance for your suggestions.