Which computer for digitizing and streaming?

Keep recording separate from playback in your requirements. Once you have "ripped" your vinyl, go Mac if you want direct connected asynch USB DAC or get a Synology or QNAP NAS if you want to stream music via UPNP to something like an Auralic Aries.

Alot of users try to shut down or turn off non-essential progras running in the back ground of the computer. While I agree that any nonsese shouldn't even be installed (or remove when you buy it), so it doesn't even start up, I have found that a large number of users have puter problems they aren't even aware of (windows OS system issues), which greatly hinder performance (and eventually brick their rigs). I strongly suggest getting (you need to pay for them as the free ones identify but dont eridicate) a really good anti virus program AND separate malware program. Keep away from the popular commercial brands (mcafee/norton) and no one program is as good a 2 separate ones and sepnd a few hundred bucks on each (life time; cheapest thing you will ever buy for your rig) I like Panda - hey, being we get hacked by china...

Puget Custom Computer built mine. I use a 5-year old Serenity from them (a core i7 running Windows 7 with all solid state drives). It's a very quite machine with little heat and has has proved to be very reliable--no hardware changes at all and no failures in very heavy usage for music and everything else daily all this time. And if I have a question, they talk to me on the phone, all these years later. PCC is great and I will buy from them again.

Hi, I'm getting started on pc audio, and still not sure what software is best for a retiree and an idiot on computing, but one thing for sure is the standard windows media has worked for me so far. I have however noticed differences in sound from different computers. I have 3 different laptops that I use with my main gig and they all sounded different.
I believe what "rgs92" is right about getting a dedicated computer for the best result.

I'd go with a Mac Mini. Matter of fact, I did. 

You could go with a Windows-based platform, but I think you'd spend a lot of time trying to squeeze performance out of it, and to figure out what went wrong. A dedicated Mac is just much easier and less prone to issues, IME.

Get a Mac Mini, set it up with an old monitor, keyboard, and mouse. Then put it on your rack to run headless, controlling from an iOS device such as your phone or iPad using Apple Remote, or from any other Mac in the house via Share Screen. (You'll need WiFi, of course.)  Lots of info on the internet about how to do this, and optimization is easy.

For the Mac Mini, get one with an internal SSD drive to reduce mechanical noise. Use the SSD only for critical software and OS X. Then get an external HDD hooked up via Firewire 800 or better, or if you're feeling more ambitious, an NAS. Benjamin at Mojo Audio does a good job of using an AV drive in an OWC case with modifications.

After you've established your library -- in iTunes, most likely -- you'll want to use iTunes only for library management, as it's less than optimal for sound. I use PureMusic and love it; Channel D also has Pure Vinyl which includes PureMusic but is more geared toward vinyl reproduction. You could also use Amarra or Audirvana, but the thing to remember is that you want software to pull the files out of iTunes and handle them properly.  BitPerfect is a clean and inexpensive option as well.

All in all, this is all about setting up a dedicated system to do one or two things well, and then tuning it to just do the basics.  It's easy; it's a one-time thing, and the results are fantastic when done correctly. And you won't have to get up and down for each album side!

PM if you need more info.