I'm not the guy to advise you on parts, but there are experts here who can. I will offer that you'd be well advised to ignore any flat tappet cam, and focus only on roller cams. Today's oils, other than a handful of "racing" oils marketed, are stripped of zinc and phosphorus which are critical to the life of a flat tappet cam. Also don't fall into the marketing trap, selecting the cam for the way it sounds at idle (thump, thump, thump). You can easily have an engine that "sounds mean" at idle, but doesn't have the power to pull your hat off in mid-range and above. Like you say, the cam is the heart of the engine, and you've got to coordinate your block, rotating assembly, heads and gaskets and then select the optimum cam.
There's been a ton of threads on here for BBC build advice, but the guys who know the magic generally jump in and explain soup to nuts. Good luck on your build!