Dude do it! If thats the type of beer you like, thats what you should brew
I freakin loooove Belgian beer. If i had a my way, I'd drink nothing else
Seriously. My current commercial stash is this:
Now regarding your tripel....ok just deleted a big chunk of my post (thought it was AG). The only problem with this kit is that its extract. Extract is all good, done some awesome extract brews. HOWEVER! Extract will end up at a much higher FG than you really want in a tripel. For example Westmalle is basically the beer the style is based on, and finishes at 1.008. To get your extract more fermentable I suggest you get some 2-row malt and a hop bag. You basically want to do a mini mash. chuck your extract in a decent sized pot with some water, and add your 2-row (probabaly german pilsner or something light) in medium sized hop bag once you get to about 70 degrees C (sorry... metric system is the ****). Mash/steep it at 65C for an hour. Then do a short boil. Might sound complicated and long winded, but basically you want to try and get your extract more fermentable, otherwise you will end up with a lower apparent attenuation (higher FG). Alternatively you can skip the grains and use beano or "dry enzyme" at the same temps but i cant suggest any quantities, havent used it. Either way you want to boil it after to get hose enzymes to sod off.
Basically either process will release some enzymes to break down the more complicated sugars into stuff that will actually be used by your yeast.
If you just go with what the kit suggests it will probably turn out fine, but if you've actually had a decent amount of good tripels, you will notice the difference immediately.
Your fermentation temps are kind of important. Obviously, they affect flavour, but also your attentuation. If you can, start it cool at 65F (you really dont want to go much lower). Leave it there for a couple of days, basically until you start seeing it slow down. You then want to try and raise it by about a degree each day till you reach about 75F. This will help keep those yeasties going. As someone has already mentioned... those times mentioned for secondary fermeter/conditioning are rediculous. Just leave it for 3 weeks in the primary then bottle those bad boys. Let them carb then "lager" them till they are popped.
No expert in the style (or home brewing) but i learnt a bit with my last two tripels.