I still have yet to complete my costume. Money is tight! But I will finish eventually!
As for the velcro and how it's sewn to the vinyl, I basically just followed the boot tutorial on the forums here and looked at the reference pictures on the gallery here.
The photos on here are the most recent pictures of my boots that I have. For the grooves, I just studied the reference pictures closely, counted how many "grooves" there were on the original shoe, and compensated space on my boots so as to have the right number of grooves. I first drew them all out using a pencil, and then used a normal x-acto knife. My process for each groove was to score along the pencil lines I had drawn with the knife, and then slowly cut deeper with each pass. After I got to a point that I thought was deep enough I would leave the knife where I cut down to, then angle it to cut across the the other side of the groove. This way I got an even depth across the whole groove. The smaller ones were kind of tricky though.
This is by no means the "official" way to do it, nor is it the easiest. It was just kind of what I did haha. I am sure there is a simpler way haha. Hope this helps!