I totally agree - start with your smallest kite first. Maybe 7m. I have a 10m but its more for start/end of summer, and for low wind days. Im lighter than you, so use a 6m for summer.
You dont want to be overpowered as a newbie - buy the small kite first. Ask the kite shops for demos and find the brand you like.
Theres a LOT of choice out there, so do your research.
Also, check the estimated wind range of your kites (as in link) and compare that to what wind you get in your area. Cape Town mostly nukes at 20kts and up in summer. Lastly, remember that different kites have different power, so size isnt everything, design counts for a lot too.