Yes you can use a long action for your build as long as it is a MAGNUM action. And as for "Leads" you mean bullets, you have a ton of options. I see alot of guys shooting the 168 bergers for their high BC and effectivness on game. Nosler Accubonds are great too. Do you have an Idea on which barrel you are going to use? Optics? Stock? Good luck.
" People sleep peacably in their bed at night only because rough men stand ready to do violence on their behalf " - George Orwell
I am the way I am because I watched the movies "Red Dawn" and "Tremors" at a impressionable age.