Hi Rillis
Can be a little confusing cant it? I recently was asking the same question a few months ago when I was buying my gear. I'm about 110kg, in Brisbane area, kite at Sandgate, Gold Coast & Sunshine Coast.
I found there were 2 trains of thought, particularly if you are only starting out and having just the one kite (as I do).
a) bigger kite, but you will most likely get kicked off the water quicker if the wind picks up.
b) smaller kite, with maybe 2 boards (one a dedicated light wind board).
I went with option b) and purchased a 12m Cab Switchy instead of the 14m, based on advice from my instructor and a few others here on SB.
I have to say, so far so good and I believe it was the right decision.
While learning, I have found most of the time to have enough power on my 12m and in some cases overpowered.....more so than being underpowered.
Obviously conditions are the determining factor, but technique has a lot to do with it, and edging hard to hold down the power essential. My normal stance is fine, but I'm still trying to master edging hard while riding switch. Generally I have found my 12m to have more than enough power while progressing through these early stages of the learning curve, and think I may have struggled at times with the power on a 14m. Unless of course its light in which case, not many kiters are out anyway. I have never flown a Zeph, so cant comment and similarly I have yet to buy a dedicated light wind board for the lighter days, so cant comment how much difference that will make either.....thats the next purchase

currently my one and only board is a Slingshot SX 143cm.
My only advice is, wait till your finished all of your lessons before purchasing, talk to as many people in the meantime as you can, check out the sizes of kites being ridden at your local, particularly by us "bigger guys". Get out there have fun, stay safe, its addictive and no doubt (just like me) you'll be thinking about expanding your quiver ASAP anyway