STOP.
Now think.
And now some more.
What type of crazy person would strap themselves into a power kite with NO idea how to fly it, how to use the safety systems, how to set it up and go into the open ocean with it. (if they get father than the being crumpled in the sand dunes.)
If kites start around 1500 new, what does a 150 second hand one suggest?Top of the range, latest model, highest safety equipment.Or. Outdated, not as safe,possibly damaged equipment.
I think windsurfing harness will be fine initially. My dad used his for 7years of kiting no worries. (recently upgraded to kite harness after my constant hasseling and LOVES it)
People die kitesurfing, two deaths i heard of lsat year alone. People get badly injured ALL the time.
Get some lessons, and your instructor will tell you EVERYTHING you need to know and more. Plenty of instructors floating around here. Get in touch with them, and get lessons.
Our sport is and has always been at risk of being banned due to danger and accidents caused by various people. Lessons will minimise accident chance.
Also, surfboard will be fine, dont worry about straps.
So to answer you question, all you need is a kite (some string helps also

)