Hi Fernando and Jen! Really glad you guys had fun with your lessons yesterday.

I personally use ONeill Superfreak 3mm booties and haven't yet had a single urchin go through, although that didn't stop the one that i sat on! I've had those booties for 4 years now and were the best money i've spent... especially given i'm in the water almost every day at the moment teaching.

The ones to look out for are the ones that have a nice thick double lining on the bottom of them. To test them out i usually bend the soles of them; if they feel like they've got some nice solid rubber in there they should be good. I'm pretty sure the Mystic booties have the same good thick soles as my ONeills.
As for buying gear, there are pro's and con's to new or second hand.
Harness - new. You only sell a harness if it doesn't fit, is uncomfortable or is falling apart. Harnesses mould to your body after a couple of uses so your better off spending a little more and getting a properly fitting comfy one for you.
Board - either new or second hand. Your first board is just a board. As long as it's a kiteboard thats the right size (~136x42 for you guys) then it'll be fine. After a season or two on the water then you might like to shop around for something specific, but until then, almost anything the right size will do. That said things like footpads and straps do wear out and board can weaken and snap if old and had a rough life.
Kite - here's where it gets tricky...
Second hand+ It's cheaper
- It's condition is unknown, which is worse if your inexperienced as you don't know what to look out for
- It doesn't come with any support
- Possibly beaten up and worn out kite which could end up costing heaps to repair or fix just to keep it holding air and flying
- Older safety systems can be a bit iffy
If you do go second hand then make sure it's newer than '08 and looks like its in good condition, no repairs and holds air when pumped up.
New+ It's new
+ You get after sales support from the shop you bought it from
+ It's got a warranty
+ Brand new safety system (really can't stress this enough, things have changed a lot even in the last 3-4 years)
- Costs you a bit more up front, but will last longer
My recommendation if you want the benefits of new without the price is to try and find a kite that's on clearance from the previous season (2011 model). If you buy it from a shop then you'll still get the after sales support but it won't be as expensive as a brand new 2012 model kite.