Hello Mike,
I can't help you with the sizing information, but regarding versions : If you have someone, who is willing and able to dig into forums, wiki and PDf files, cope with XML, AMPs, FTL Templates and maybe even learn a bit Javascript, Freemarker and Java and ask Questions in the forum, and havfe a decent backup, then you dont necessarily need the enterprise version. Alfresco runs fine, basically. But sometimes it might be necessary and you need someone, who is not scared from looking into technical discussions & wikis.
Regarding your requirements : its Alfresco Standard, I cant see much "extra" stuff in your list (yet), but you should think about that again.
In Detail :
To replace your networkdrives with Alfreso, simply launch Alfresco, connect a network drive via LAN and copy your structure into the system.
Now you can administer the access rights in Alfresco to your desire. The users will only see those spaces, which they have access to. So you could have an internal repository plus a folderstructure something like
/trainings/class1
/trainings/class2
….
Wiht "class1" having a set of files and links to files & spaces, which are part of the class.
The most tricky parts will be : Do you want to manage all students separately or just 1 user/password per class? And do you want all your content on a system, which is reachable from the internet and do you want the students to "collaborate/communicate".
* If you want basic collaboration, you may want to use Alfresco share.
* If you just want a very basic forum function and workflows, you can use Alfresco Explorer
* if you wand better wiki, blog, and forum activities - use Liveray portal as Frontend and integrate Alfresco Explorer Spaces only
* if you dont want any collaboration - build a website and deploy the contents with the WCM components. So the "internal" client is for VPN Users only and the class-documents are available for any website user (maybe with login).
For Share installation :
* You can split alfresco basic & alfresco share between servers and only allow share to be accessed from the internet.
You will spend quite some time installing and adapting your system for you, though. It will be up and running for the first time quite fast, but to finetune the system, finetune your space structures etc, it takes time and you probably will to it more than once. Simply because you can you so much with it, you will discover a lot "Oh, I want that too"s. So it might be helpfull getting someone into the project, who knows Alfresco already.
For instance, the email-gateway function will be really neat for you, I think. You can provide spaces with emailadresses. Every Email, going there will be inserted into the space as "content".
Hope that helped a bit.
Norgan