Is it possible to use HALion 6 in Dorico like Halion SE and HSO? I’m not very good with playback templates.
It’s totally possible to use Halion 6, but not like HSO+HSSE, which means you’ll have to create new end points, with expression maps, etc. Which is not compatible with the end of your post, I am afraid.
Could you tell us exactly what it is you want to do? Maybe that will help us help you 
Recently, I spoke with a Film Scorer, I asked for any tips on my compositions. He said that as a Film Scorer, you want your scores to sound as real as possible. Similarly, he also said that my compositions sound too electronic (using HSSE). So I would love to be able to use HALion 6 instead, more instruments, more appealing sounds, etc. Unfortunately, I’m not sure how to create playback templates from scratch and it seems very intimidating to me.
HALion doesn’t provide any particular advantages over and above any other sound library’s plug-in. It’s all about the sounds, more so than the plug-in. So you should focus on the sounds you want to use, and then learn how to use those libraries. Focusing on HALion itself won’t get you very far unless the sounds you want to use are in HALion format.
HALion 6 would be the most affordable option at the moment I believe. I would want to use those sounds for now and further invest in libraries in the future. Although, the videos and explanations I’ve seen on how to create playback templates seem overwhelming in all honesty.
The important thing is to pick the sounds that you want to work with, rather than the plug-in. If you’ve explored the sounds that come with HALion 6 and think they are the best choice for you to produce the kinds of film scores that you’re wanting to make, then that’s great, but I think (without casting aspersions at HALion 6, which is packed full of interesting and useful sounds for all sorts of productions) it would be an unusual choice for somebody who wants to produce full orchestral mock-ups.
What is also worth mentioning: HALion Sonic SE can play all sounds from HALion. So unless you really want to tweak or create new sounds directly in Dorico, you can just stick to using HALion Sonic SE. In that scenario HALion just becomes the content creator and HALion Sonic plays it back. Does that make sense to you?
I have to extend the range of most instruments in Halion 6. Is there a way to use the HS0 playback template with Halion6? I also tried to safe the Endpoint Configuration but I can’t figure out how to load it in order to use it for other pieces.
Unfortunately not at the moment, no. We do plan to make it possible to use either HALion Sonic or HALion in this way with Dorico, but we’ve not yet implemented it.