My company makes some medical software, up to now we just manually install our stuff onto an Dell or HP server, or the client provides us with a VM and we do our thing. 

I want to automate the process and build a standard Windows 7 image that we can apply onto the same HP box each time and quickly build new machines. 

I've used Sysprep\ImageX in the past and am familiar with Altiris etc for large scale desktop rollouts, but I'm  a bit stuck here as to the best approach. At my last role we had volume license keys and obviously a SA license with Microsoft. But here we're pretty tiny and use MSDN Subscription licenses for our own machines, and OEM licneses for the clients. 

So should I engage MS about a volume license that I can use to create images that I deploy on boxes that go to customers? 
Or are we infact an OEM, who is modifying an OEM box (HP Mini) and therefore I just need to use the OEM license that came wtih the box? 

If its the latter then I assume I need to just follow the OEM image build/deploy process and undo what HP has done already by adding my own medical apps to a new custom image. 

MS licensing never make sense to me so just hoping someone here knows the right path I should go down.