If you're in it for more than the looks you definitely want to go custom. There's little point in water cooling when you push yourself into a closed-loop only mindset.
If you're not extremely limited on space, there's *no* reason to buy a closed-loop watercooler like the h100i over a high end air cooler.
On the other hand, a custom high end watercooling setup can yield dozens of degrees C difference over high end air. It's not effective dollar for dollar, of course, but the cost is justified for some.
Custom loops can easily last 2.5 years and can be expanded for GPUs with universal blocks. That's something you can reuse for build after build. There are plenty of people with custom loops who have parts dating back more than a decade. It takes some maintenance and careful part selection, but it's possible. A raystorm kit is a good starting place, but you will want more once you get it together.
I would start doing research on exactly what you'll need for your setup to be happy with it once and for all, then commit to it. As an example, you may have 2 GPUs later, so definitely look into a 360mm radiator if you can fit it.
You may want to get plasticizer free tubing to prevent build up in your blocks over the years. Kits don't come with that.
You may want a quieter/more powerful pump than comes with the raystorm for adding SLI later, etc etc. There's tons of research that goes into doing a custom loop, and that's why there are so few who actually commit and do it.
I'm not going to be the one here who says, "Yeah man, the H100i is awesome it's almost just as good, forget the Raystorm kit."
That's just plain disillusionment. If you want to get the H100i just to say you have watercooling, then ok. Do it. Just don't forget that the setup is neutered, compares unfavorably with high end air, and can't be expanded. In other words, a giant waste of money.