I am new to the 454 & new to the large/small primer idea. Is it simply a matter of pick one & roll with it? What are the necessary considerations of each?

As I recall, when I started down the 454 Casull path over 30 years ago, small rifle magnum primers were recommended. I want to say that Freedom Arms specifically recommended the Rem 7-1/2...

7.5 rem works fine. As does cci large pistol mag primers. Its not much of a thing. Go with whatever brass you can find and load away. Both work well with any loads from modern manuals. Back when the 454 was being pushed much harder, SR primers had their place. I have loaded and fired more rounds from a 454 than I care to remember over the years using both. Neither one gave me a reason to stop using the brass that utilizes either of them

All my handloading for .454 Casull has used CCI small rifle magnum primers, always with good results.