Dave, if you get the time to attend a Big Game Rifle shoot at an SSAA range, have a chat to the boys & ask if you can shoot a few different types of rifles/calibres to see how you go. I don't know how much of the larger calibres you've fired but this is the best way for "starters", you might be lucky if they're doing an event - you might get dropped in a whole event, good crew.
If you find this is the way for you then i suggest to start with a group 1 rifle & work from there.
Google it & read the events etc, I'd hate to see you purchase a big thumpa & then find its not your cup of tea - work up slow.
Welcome to the forum, this place will certainly make you envious.
Yes you can do a .500NE on a Ruger No1...a few about in NQ
Regards
93x64mm