IMO, yes 10GB is more than enough space for your average Blu-Ray movie to be encoded to h265, and that includes keeping the DTS-HD MA 7.1 or Dolby Atmos Audio. Others will disagree. 
My recommendation is to do something simple, like consider picking a movie you know really well. Use video settings of h.265 10-bit (NOT using QSV, if that’s an option!), 1080p size, constant quality of RF 20, Constant Frame Rate (“Same as source”), and then for the audio section, choose passthru for the big audio track like DTS or Dolby. If you want to keep subtitles, you’ll need to choose the PGS ones, and you’ll also need to choose the MKV container if you do that. Otherwise, MP4/M4V or MKV are fine.
Maybe encode the first three chapters and how long it takes, and how big the file already is. Remember that if handbrake encodes a film at 24 frames per second, that means it will encode at about real-time (film is 24 fps!), so a 2 hour movie would encode in 2 hours. But be prepared for lower frame rate encoding speeds with h265.
Going back to the video options in handbrake, if you use the constant quality setting (RF20 is just a starting point, but it should be pretty good for 10-bit h265), remember that every movie will have a unique file size, even if they’re the same length. It’ll use more bits for complex scenes, and fewer for simpler ones. A good rule of thumb: The more grainy the film is, the larger the final file size will be.
Then review the quality of the encode. How’s it look? Does it play nicely (Direct play or direct stream) on all your devices? If you’re happy with it, and the time needed for encoding, then try encoding the whole thing, and find out how big it is. It’s a learning process, but this would at least give you a place to start.
Random tip: If you plan to stream these remotely, there are options to encode the video (or an extra copy!) to stay within a set bandwidth limit, like the default 4mbps or whatever. But that’s another day once you try things out and see what you think.
