Coming from the double world, I'm thinking 1 + 3 is plenty. Then again, I don't see a man-killer in my near future thanks to COVID travel and economic chaos. Heck, thinking about a plains game trip to Africa, the only flights I see on Delta right now go through Europe which is a real turn off for me (I love traveling in Europe but, using Europe as a layover is not good IMHO even if my rifles make it to Africa in serviceable states!).If a guys is going to the trouble of building a 404 Jeffery, I think it needs to be a 4 down/drop box magazine. If not you blow a little bit of 404 cool, buts that’s just my take.
Hippos and Buffalo aren't on my trophy 'bucket list' so, I'm good there. If I win the lottery and become able to afford an Elephant, a new rifle would be pocket change assuming I don't use my 470NE double.
That leaves big cats and other things which are honestly a long ways off too. For big cats and large plains game, I'd probably do a 375H&H or some other similar option which is probably 1 + 5 (possibly 6) though the 358 Norma Mag would probably be a viable option as well.
As a "ONE AND ONLY" rifle, a HEYM Express bolt action in something like a 450 Rigby would probably be my focus today though a 416 Rigby would be a good one as well. I do occasionally think about selling the 470NE double because the hunt it was bought for is very unlikely to happen now. If things change, I could always replace it if I go for the Big Five with a lottery win (come on PowerBall!).