1.) Continental Europe is good for most Europeans. Great locations include UK, Germany, France and Netherlands.
2.) Yes, US will provide AU/NZ members a better experience. Europe pings to AU is typically higher.
3.) Unfortunately, you're facing the same problem most game servers face: geographic latency. You either have to split your US/AU/NZ and EU players to 2 different servers close to them, or someone has to live with the increased latency - you decide.
I suggest you to hosted in Europe as majority of visitor
█ MultipleCloud - Multiple location hosting provider
█ 200+ worldwide location | different server | different ip owner | best for pbn
█ BigfootComputing - Dedicated A/B/C class ip
█ 100% no bad neighborhood | private name servers
Agree with the above, Europe location would be best for the majority of your visitors, if you host with somewhere decent, you can get pretty good coverage of 100-200ms from the US to a Europe based server as well, Australia will be higher though. My recommendation would be to use a CDN as well to speed things up.
█ WebSound - Affordable, Reliable Hosting Solutions
█ High performance hosting solutions located in EU, NA and the US
█ UK SSD Web Hosting / UK SSD Reseller Hosting / Minecraft Hosting / VPS - www.websound.co.uk
+1 for the CDN, that should solve (or at least alleviate) the issues for everyone
█ CanSpace Solutions - www.canspace.ca - Canada's leading domain registrar and web hosting provider
█ Premium Canadian Web Hosting and .ca domains. Trusted by Canada's largest corporations
█ Affordable Web Hosting | 24/7 Support | CIRA CERTIFIED | Proudly Canadian