you think I'd be better off with a media server.
Actually yes.. media server is exactly the right way to go for your situation.
If you are going for the Apple solution then the PC is not highly useful.. Let me leave it aside .. you can play games on it etc.. but it is really better left out of the equation.. and you can just keep one of the external drives plugged into it for your backup. You can use the PC if you step out of the Apple media setup and use it as a media centre if you want. But not using iTunes. At least for videos.. music on itunes is ok.
A Mac Mini is a great media server. You don't have to buy a brand new one.. In fact they are way overdue for an update so not good value, but you can pick up a 2012 mini for $400-500. They have 4 USB3 ports which is really why this model is better. The 2011 is not that different and a bit cheaper on second hand market. But they have USB2 which is too slow. (FW800 is good but too old and thunderbolt is still far too expensive). Still there are ways and means.. you can buy adapters but they are usually more expensive than simply paying the bit extra for the 2012 model.. try and get one with 8GB RAM.. the standard 500GB hard disk is ok. (I always stick an SSD in them for boot drive but that is to run it as a computer not media). It is almost completely silent. You can plug your drives into it, load it up with your media and share that media to the network. The mini sits with the TV (hdmi output direct to the TV input) and Stereo. It can network connect by wireless to the TC or by ethernet.. the later of course is always going to be the better choice.
See Understanding Home Sharing
iTunes: How to share music and video
I am not entirely sure what you mean by cloud access. Anywhere in your network you can still connect to the main router by wireless or ethernet, and use cloud services.
You can use an airport express or Apple TV next to your drum kit for streaming to that location. You can use airplay via the ipad to control that. (That is getting beyond the level of my experience I warn you .. but it is sure possible to do.) The less wireless you use the better.. but as long as major items are connected by ethernet then streaming runs pretty well.
There are other cheaper ways to do it. But you need to step out of the Apple methods. Go for a WD live TV, which is amazing little box. It can pick up your video collection on the vista PC and play it to the TV. You can plug a USB drive directly into the WD and have it run its own library without streaming at all, but it can share that USB to the network so you can load videos to it.. but you don't use itunes to do it. To play itunes audio it is easier to simply use your ipad etc. but an express can also be used if you want to do it neatly by wireless.
The TC itself is fine to keep for TM backup of your Mac and as wireless router. It is not so useful as a file store.. and I would not really use it for that.
This is very much open to discussion and I am sure if you talk to different people they will come up with different methods. The problem with large media collections and new laptops with small SSD has not been addressed by apple due to all the copyright controls in iTunes. A simple NAS running itunes server would be fantastic.. for now the mini with loads of USB drives is the closest we can get to that. But the cost is not bad albeit the integration not as good as the newer media aware NAS.
