As of 03/15/2016 the Spurs have clinched a top-four seed and the Southwest Division along with HCA in the Finals against any Eastern Conference team other than Cleveland or Toronto.
The magic number to clinch a top-three seed in the West is one. A Clippers loss tonight would do it.
The magic number to clinch a top-two seed in the West is four (though the two upcoming games against OKC are worth two points each and five points together). There's no scenario where the Spurs would go into the GS game having locked a top-two seed, but there is one where they could clinch even with a loss on Saturday.
The magic number to clinch HCA over Toronto in the Finals is five (though the game against the Raptors is worth two points given that the Spurs have already clinched the second tie-breaker).
The magic number to clinch HCA over Cleveland in the Finals is seven. The Spurs currently lead 22-5 to 20-7 over Cleveland for the tie-breaker, but the Cavs can still bypass them.
The magic number to clinch the Western Conference first seed and the top overall seed in the league is 20 (though the games against GS are worth two points separately and a total of seven points together).