There’s really little reason
There’s really little reason to pay extra for the i3-2105 over the i3-2100. Yes, it has HD Graphics 3000 vs. 2000, but unless you’re gaming, it won’t change your experience. If you are gaming, the 3000 graphics will likely not be too satisfying.
Sure, a Gen. 3 SATA III SSD is better to have, I don’t think you’ll notice much difference in practice with an HTPC. The big jump is really going from a HDD to an SSD in the first place.
SATA III isn’t going to have any meaningful effect on power consumption.
The case should have plenty of airflow. You should ask yourself though if going fanless for your PSU is truly worth the price. The 380W S12II is MUCH less expensive ($75 vs. $130) and uses a large 120mm fan although it is not modular. I have the 330W version (no longer sold) and I can’t hear it over other fans. Your system noise is all going to come down to what is the loudest component in the system and how high it is above the noise floor of your room. Don’t get me wrong, I would love the supply myself, but it may not really make a difference for you.