For my HTPC case, I want something less than 10” deep, and less than 12” tall and not too wide. The Lian Li Q07 fits the bill perfectly. The computer will have an Intel G530 processor, a dual channel TV card, probably a blue ray drive and one, and in the future more hard drives. I'll use integrated graphics. My key question is what to do for power and cooling. Quiet is mandatory, and the PC will be on 24*7.

I have few ideas:
A pico power supply. I'm unsure, but I think I'd want 150 watts to be safe. Cheapest I found this was $95. I'm concerned that the voltage will not be as steady as with a regular ATX seasonic supply. But I'd then have space to fit a monster vertical 120mm heat sink and ultra quiet fan in the case.

Or fit a regular seasonic 300 or 400 watt ATX supply in with a horizontal cooler – the coolermaster geminii S will fit with less than a cm to spare. I would duct the power supply to the fanless heat sink, which would then suck the warm air through the heat sink and out of the case. I'm worried that wont keep things very cool, and could be loud when the processor is stressed. But I'm confident the power would be smooth and I would obviously have plenty of headroom to add more drives and other devices in the future. Certainly more than could fit in the case. I could get a modular 400 watt PC Power and Cooling for $50 after rebate.

Or fit a SFX or TFX seasonic power supply. That would give me a bit extra room inside the case, but it would be fairly useless space since the heatsink couldn't be enlarged much, and the smaller fan would do a worse job of taking heat away from the CPU. So I might need another fan. I don't like this idea.

Thoughts?

You don't need a monster heatsink with a G530 unless you want zero fans. It doesn't run hot, especially if you underclock it a bit.
You should be able to manage with a case fan and a reasonably-sized fanless heatsink. If your case fan is too far away and/or spins too slow for that, why not use a quiet heatsink fan? You've already got a fan (and at least one HD I assume considering the size of your case)...
I don't know where you live and therefore where your electricity comes from but, if you leave the machine on 24/7, it'll waste electricity. Why not use standy? Regardless, with an inefficient PSU will waste more. That's one of the advantages of a pico.

It will serve as a NAS and media streamer to other computers / devices, hence I'll want it on 24*7. Some of the devices (a grace digital player) can't wake it from sleep, at least I don't think so - I'll look into it.

I like the idea of a pico power supply, I just would hate to spend twice as much for something that is less reliable. It <might> be a bit more efficient for my usage, but I trust a seasonic powersupply more than a no-name 12v brick supply. In other words - I'm hesitant to go pico. I like the idea of no noise though.

Premium picoPSU-150-XT/12.5A 150W AC-DC $83 (this is the exact model i bought)

If you go with an intel mobo + Mugen 3, it will allow to spin down the slipstream to 250-300rpm (in bios), to me inaudible. My HTPC has one running and even though its i3 2120 even at load it doesnt exceed 60C. Another option is Thermalright HR02 Macho, much more massive, and probably better cooler for low rpm fan, but TY140 will not spin that low, 700rpm is the least i was able to, but you can always get another low rpm like a Scythe Slipstream PWM 120mm Case Fan SY1225SL12LM-P (200-1300rpm).

I have no issues with 150XT powering my i3 2100T (six months 24/7 and no issues), mine even at load consumes 50W, a G530 should consume less, not sure how much would your tuner card will consume or the additional hdds you will add, but i think 150XT should be more than enough. Personally i would recommend to check Q11, similar but slightly bigger than Q07, and use the single 140mm case fan, swap the frontal fan or undervolt it, probably 300rpm would be enough for a big tower cooler on it.

Dimensions
Q11 10.24" x 7.87" x 12.40"
Q07 8.19" x 7.60" x 11.02"

Here is a couple of pics to see the difference in size between the Q11 and Q07, pic1 n pic2

The tuner card will limit the orientation of a tower cooler (check my minimi build on my sig), the HR02 is asimetrical (it starts almost flush on cpu socket and grows to the back) so if you mount it like i did, it will still allow you to use the PCI slot (i think, i dont have 16x slot to know for sure, the macho has a new mounting bracket), but my guess is you cant use a fan with it, thus recommending again the Q11, out of the fan will cool draw cool air inside the case, because of the postive preasure it will also draw away warm air outside, and it will also cool the CPU due to proximity of the CPU socket to the frontal case fan. Here is a pic of the HR02 + Lian Li Q11,

Yeah, without underclocking a G530 would be considerably cooler at load than a 2120.
Perhaps Abula could briefly underclock his 2120 (it can be done in software) to the speed of a G530 and tell you want temperatures he's getting relative to ambient.

I forgot the question about 150W. Abula is of course right that 150W would be fine but you could be fine with a considerably less powerful PSU as well. If you want to know how low you could go, you'd need to know the power consumption of your TV card and any USB-powered peripherals you want to attach.

The nice thing about a 150W (or more) PSU and a monster heatsink is that you can upgrade the CPU later.

Thanks for the responses.

I like the Q11, but it is too tall for me. Unfortunate – I wouldn't mind the built in fan. I might go with the 08 – I would like the built in fans, and once I have more than one hdd – I would not have to jury rig it in place like I will with the 07 which only fits one. Then again, jury rigging suspended hdds would be quieter.

I think I will go with the pico power supply since so many here have had good experiences with them.