1. Leaf spring steal is just fine... My Himilayan Imports blades (and fine blades at that) are leaf spring steel.
2. You would have to break the heat treat on it... (heating is and hammering is out... or buy a sheet at the thickness you desire...
3. Heat treatment is the easy part... harden/quench in water, oil(look out for fire) or clay?
Personally, oil sounds cool, but clay give the hammon
Khukri may be ambitious for a first blade... but you may as well start with something... wost case you learn and wasted $2 in material, and some time...