Bring EuroHash back to its roots: an event mainly for Europe-based hashers.
Reduce the number of participants to 300-400 hashers.
Open registrations 1 year ahead - not 2 - after you've registered your non-for-profit, opened a dedicated bank account and finalized your budget.
Use registration software that requires payment at the time of registration, therefore skipping the time-consuming financial reconciliation step.
Consider the option to let hashers deal with accommodation themselves, do recommend a hotel or two and a hostel (and perhaps make a deal with them). Maybe there are campsites near by.
Choose a location from where you can reach the run site by public transport, thus avoiding the hassle of arranging buses.
inform - inform - inform
Let your participants know what you are up to. Have a web-site that is well structured, complete and update it regularly. That way you avoid an endless and time consuming stream of requests for information. FaceBook is not the right medium for that (it serves other purposes).
Keep close and warm contact with organizers of earlier EuroHash events. Use their expertise, the shortlst above is just a short-list, there are much more things you need to think about.