Here is a very old opinionated reply. Nobody needs a modular power supply, they don't work any better than the other kind. And 600 watts is okay, in fact it's more than what you really need. But it's a good investment.
The really big question is why you're spending so much money on a graphics card. This is your first home-brew computer. Graphics cards can drive you crazy. Get the Graphics card later. Many motherboards today have video chips incorporated into the motherboards. Most of these do not work or feel great, but do not do any harm either. In my opinion. Same for the network card. They now come with network card's built-in. Get a good, but not overpriced motherboard.
The most important choice you make is which CPU you to buy. In theory you can always upgrade your CPU, but in practice is very expensive to buy a new CPU and possibly a new heat sink. So put the money on the CPU and the heat sink. They might last longer than the motherboard.
About the case. Just get a standard case. Unless you are short on space under your desk. Standard cases are easier to work with.
Like I said, this is opinion more that fact.