I did try applying PVA with a sponge on the first attempt. It came out Ok but I did get some imperfections. This was probably just me. I found it a lot easier to spray but I have heard of loads of people who use a sponge including the people I get my fiberglass materials off.
And yes banging can cause cracks. I have always done it that way because that is the way I was taught when I did my course. I have been lucky so far.
I think everyone develops there own way of doing things and will have their own good and bad stories to tell. I used wedges on my first attempt but no matter how hard I tried I couldn't get them in without leaving some marks.
On the course I did, I was told to leave the mould at least 3 days at room temperature. I have always left anything I have done around about a week. This works for me. I would really recommend Farecla G3 Liquid. It really does put a shine on the finished product.