I really liked your suggestion of starting out with a tiny system for the crown (tape attachment probably).
Then, every month or 2 keep increasing the size of the piece.
This is good for:
1) Good for the wearer so he can learn slowly.
2) Good for the close friends/family/collegues cuz they will not notice.

The hairline. . . and getting it to look great is something that takes daily time/effort to master.
On the other hand,
I was experimenting with the following hairstyle: Left part with hair going forward. It looked very natural and the hairline does not have to be perfect.
Used tape like walkers and where the part is I used ORWG (glue) like 1/2 inch.
Nobody gives second look cuz my piece is thin enough so you can see scalp.

My 2 cents :-).