I have two builds for a HTPC. I want to buy somewhat soon maybe in the next month. It will need to play 1080p playback of some home videos and I want to learn to stream my TV through it. I'm pretty set on mini ITX but I can be persuaded to go with Micro ATX. I already have a WD green 1.5TB hdd that i'm going to use. I'm pretty set on the i3, from what I know its a good CPU.
So I guess what you really want to know is do you go for a quality motherboard or a cheaper motherboard that has the convenience of WiFi onboard.
I'm going to place my vote for the Gigabyte with the add-on WiFi. Anandtech's review of that board was very complimentary. Plus, it has USB 3.0. I have no experience with Zotac. I do like their idea of bundling WiFi on their boards, but reviews are always mixed on their quality. The Gigabyte is a sure bet.
For the PSU, I think you can get by just fine with the 150W as long as you use the onboard graphics. Even if you add a TV tuner, you'd probably be under 100W. You can also get a 160W (200W peak) pico PSU here. That would move the power supply out of the case into an external brick which might help with your build and it is 100% silent. That would give you an extra 10W too if you really feel you need it. The Antec case you've selected already has the small round cutout required for the pico psu DC plugin just above the I/O plate.
Also, have you looked at the Antec ISK 310-150 variant of that case? Same case but it's silver and has a smaller cover for the optical drive. It's $10 cheaper than the black.