Those boots look ok to my unofficial eye, but you'll need to cover up the sketchers logo on the back heel as well.
You might not be searching properly for the spats. To my knowledge, most people use antique military spats, or similar items.
This website is a really good source for inexpensive soft parts, I really like some of the pouches they have, and I just checked and they have quite a few selections of gaiters puttees and spats that would work well.
As to the belt, I'm not so sure, and it would be better for someone else to comment rather for me to voice my opinion.