I'm link you a topic on a Sokka wig that covers what you will need to do.
For the wig/materals need you lookin at this wig.
know it's expensive but it cheaper then doing what you nee on this on.
Because it a lace front you can cut the V shaped hairline into it which will give the piece the natural look. The rest of the wig you don't use for the top hair you can take the fiber out to give the side and back edge of the top a clean look. You can also use the extra wefts to thicked thw inside of the piece as Well.
Once you done the "toupee" and sew/seal it to the bald cape then you buze the top to get the right length. if their is any wefts tread showing you can go in with a black sharpie marker to mask them out.
The topic linked cover how to build the toupee to the bald cap and add stubble.