$199 is a decent price for a human hair unit - that is about what you will pay to get a unit from a Chinese vendor.
The lifespan of a lacefront depends upon the care it is given. It isn't uncommon for someone to "kill" her first unit. Also applying, wearing, removing, and cleaning the same unit will cause wear and tear over time which is why some people prefer to have two units. Another reason for having multiple units is to allow you TIME to clean the lace and hair without being "wigless" in the interim.
I have slept in units, and I have worn them daily and removed nightly. The maximum time I have worn a unit without removal was about two weeks. Whether you will be able to do that will depend upon your adhesives, as well as your desire to get to your own hair underneath.
First, remember that every adhesive will not work for everyone. The adhesion that you receive will be determined by your body chemistry's interaction with the adhesive(s). It is also common to combine liquid adhesives and tape to improve the hold.
For extensive discussions of adhesives I would recommend checking forum.blackhairmedia.com - people have analyzed adhesion, ingredients, potential side effects, etc on that site.
Silky or yaki would be my recommendation. Between the two it's a matter of your preference in texture. Curly hair is high maintenance. It is prone to dryness and tangling. It will take more care, more product and will tend to denigrate in appearance more quickly if not properly maintained.
Additionally, I would suggest you read this thread where a lot of this information has been covered.
http://www.longhaircareforum.com/showthread.php?t=254667&highlight=bobby