Can I use Mac Mini as a "server" for a MacBook Pro and iMac?

Question

I want to develop a simple system for accessing my files from multiple devices.
I heavily use iTunes (190 GB), iPhoto (120 GB) and iMovie (30 GB, but want to do more when I get time).  Additionally, I store lots of old videos on circa 10 portable hard drives (1 TB each), which I access occasionally. 
The family use all this content and we currently have a MacBook Pro and are considering buying a new computer - either a new MacBook Pro or an iMac. We also have iPads, iPhones etc and a Time Capsule. We use wireless fibre optic broadband.
I don't really want multiple iTunes and iPhoto libraries.  We want all our music and pictures in single master libraries that we can all access and update.
As there is seemingly too much data to store on iCloud, we need to find an alternative solution. 
My possible solution is:
(1) Load my master iTunes, iPhoto and iMovie libraries ("iTPM libs") on a Mac mini
(2) Buy a new MacBook Pro or iMac (probably doesnt matter which)
(3) Link the MacBook Pro(s) and iMac to the Mac mini to access iTunes, iPhoto and iMovie and the master iTPM libs
(4) Plug the portable hard drives into the Mac mini whenever I need to access the video content stored on the portable hard drives
(5) Add "users" to the system (i.e. family members), in the same way you would access a shared server at work
(6) Over time, buy more computers to access the system in the same way
My questions are:
(1) Is this system feasible?
(2) If so, can I edit the iTPM libs from the MacBook Pro or iMac?
(3) If so, what happens if both the MacBook Pro and iMac are accessing the libraries at the same time? Which takes precedent?
(4) Would this solution be significantly slower than having separate libraries on the different computers?
(5) Is there an alternative approach that might work better for my needs? (which are, after all, relatively straight forward).  When I went to the Apple store they were unsure!
Many thanks.

Answer 1

I heavily use iTunes (190 GB), iPhoto (120 GB) and iMovie (30 GB, but want to do more when I get time).  Additionally, I store lots of old videos on circa 10 portable hard drives (1 TB each), which I access occasionally.
The family use all this content and we currently have a MacBook Pro and are considering buying a new computer - either a new MacBook Pro or an iMac. We also have iPads, iPhones etc and a Time Capsule.
[…] We want all our music and pictures in single master libraries that we can all access and update.
The "update" portion of this is where your problems will arise.  You'd be better to consider your proposed system initially in terms of content "consumption", before getting into the nitty-gritty of editing shared content.
iTunes has the Home Sharing feature built-in, which solves the content consumption issue.
I don't know anything about sharing iPhoto libraries, but this KB article looks useful.
As for iMovie, I think there are two things you want to do: share the raw data (sound effects, music, photos etc.) that are used to create iMovie content; and share the finished results.  Is that right?  I'm not sure how you'd go about doing that, but if you clarify your aims in this regard, it'll help the next person who comes along.
When it comes to updating content, such as adding new music to iTunes or iPhoto, I'd suggest you do it through the Mac mini directly.  This seems the least problematic solution.  You wouldn't necessarily need a dedicated display for the Mac mini - you could use remote desktop or VNC or what-have-you.
As for speed: doing anything across a network is always going to be slower than doing it locally.  But, it probably won't matter for content consumption (though if you're all watching different movies at the same time the drives on the server may struggle, and the wifi bandwidth might be tight).
I hope this represents a good initial response to your query.