4 hit ws build

[Ryozen]

5/5 zanshin, 5/5 med recast, 5/5 OW, 5/5 iki

Assuming you WS in Rajas and Brutal, you don't need 5/5 Ikishoten merits. You can go 4/5 and leave a merit in Blade Bash or Shiki.

Also, I don't see how Zanshin merits would be worthwhile. That would get you ~1% Hassanshin, whereas with full Store TP merits you could use more effective gear when TPing and have more TP overflow for Fudo damage. Store TP merits alone would allow you to drop AF3+2 body for Juogi(+1) which has better DD stats.

So a 90 sam with a 437 weapon would need how much?

With full Store TP merits, a Sword Strap, and Brutal+Rajas in WS, a six-hit (WS+5 hits) requires an extra 17 Store TP in the TP phase.

Without any Store TP merits and the above, 24 Store TP is required.

Check out FFXI Calculator. On the "Statistics" tab it allows you to play with different jobs, delays, and Store TP options to find this sort of thing out for yourself.