Re: which reloading press?
Starting with long action magnums and working up from there to even bigger cartridges, the Redding UltraMag is probably the way to go. It's a reloading press designed specifically for what you plan to reload, i.e. the bigger cartridges but with the ability to do smaller ones as well.
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." R. Feynman. (Last sentence of the Feynman appendix to the Space Shuttle Challenger Report.)