Low Budget Linux HD HTPC

I have spent a considerable amount of time reading through thread after thread on these forums and others trying to educate myself on HTPC's.

I am going to attempt to build my own system in the coming months. This will be my first attempt at building any kind of pc let alone an HTPC. This will also be my first go at installing and extensively using Linux.

As I said I have done a decent amount of homework, but since this is a relatively expensive and time consuming process I want to make sure I have everything right before I go ahead and purchase everything. I also have a few questions that I was hoping to get some input on.

First off what I want this system to accomplish -

My primary use for this HTPC is playing video stored from the HDD directly to my HD TV. The TV is only capable of 720P so that marks the output limit I will need for the HTPC.

I do not need nor want a DVD or Tuner setup for this.

I would like to view hulu and youtube and other various online video sources.

I have no need for an optical drive of any form.

I would like to use this device as a music server and for pictures etc.

Based on my research I believe the following pieces of hardware would work for my needs:

Case - Athenatech Black Steel A100BB.270 Micro ATX Media Center / HTPC Case - Retail - $49.99

Processor - AMD Athlon II X2 250 Regor 3.0GHz Socket AM3 65W Dual-Core Processor Model ADX250OCGQBOX -Retail - $76.00

Motherboard - GIGABYTE GA-MA785GM-US2H AM3/AM2+/AM2 AMD 785G HDMI Micro ATX AMD Motherboard - Retail - $79.99

There is a comboon Newegg for both the processor and mobo which will save me $22 - combo price - $133.99

Memory - OCZ Gold 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Dual Channel Kit Desktop Memory Model OCZ3G10664GK- Retail - $69.99

I would also like to make this wireless, and I have not figured ouot the best root for this. Should I get a wireless card? or a wireless USB stick? Any suggestions as to a good one around $20 or less?

Hardrive - I have a 600 gig external I would like to start with to avoid the cost of a HDD. Can I have an HTPC with no internal HDD?
If I must get an internal I was looking at SAMSUNG EcoGreen F2 HD154UI 1.5TB SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive- $109.99

total $275 w/out HDD or $385 with HDD

What do you all think about this configuration? Will this suite my needs for the HTPC and equally importantly will Linux run well with this?

Since I do not need an optical drive I do not plan on getting one. Will this cause problems in installing the OS? Can I just use a USB drive to get this done?

Am I correct in my thinking that I will not need a video card and audio card for this device? I assume the mobo will account for this already.

The case comes with a 270W PSU. I would like to avoid the cost of buying another different PSU. I have read mixed reviews here. Thoughts?

I intend to use this device primarily with my Harmony remote. I have a USB IR module I plan to use with it. I also intend to VNC with my laptop or other desktop I already have so I do not intend on getting a mouse or keyboard for it.

I appreciate all comments and suggestions. Hopefully I have not overlooked anything, but if I have please let me know!

If I went that route I would have to get a new router. So I don't think I will go with 802.11n.

I am not sure what the difference is with the motherboards, I suppose I should look into that one farther too. Thanks for the input.