What is the appropriate size and speed for SD chips to run vSphere 6.x??

I'm hoping to get new HP DL360 G9 servers next year and put vSphere 6.x on them, the bugs should hopefully be fixed by then.

There's only one SD chip slot, sigh.

I'm wondering what size SD chips I should buy?? -- 32 GB or 64 GB??

I want to have some space for logs if needed though I'll try to redirect the logs to something/someplace else if possible.

I know ESXi needs a scratch partition and at least some log storage.

Does the SD chip speed make any difference??
I'm thinking good SanDisk SD chips, not HP's over-priced chips.

Thank you, Tom

P.S. Also looking for references on installing ESXi to the internal SD chip, I imagine it's the same as installing to a hard drive, let ESXi installer find the storage, do its thing.