There are still Row 3 sets out there. Still rocking Nuclear Data on my 'Dox and 1976 isn't very old either. If I can ever get Danger Zone off the ground with PMK we might add another to that distinguised list.
It probably makes sense to keep your original blue & gold "Vault" caps in Row 3 and if you have a base colorway for Nuka Cola (I'm assuming it's white on red) maybe let that one stay in R3 too. The rest? Match the profile with the colorway. I think these 1u caps are most likely to wind up in the top 2 rows of the keyboard for 99% of users -- preference definitely toward the function row. So if you're matching colors with an existing set you might as well match the row profile from that set too.
Do you have a "base" colorway for the Lucky 38 legend? I think the white on black might be a solid choice if you don't already have one in mind. It's very "Vegas" looking -- reminds me of a poker chip.
Here's what I'm imagining in the lineup:
Vault Dweller Pack (parent deal) - Row 3 "Vault" caps & original red Nuka Cola & NEW Lucky 38
Ascended Vault Dweller (child) - Row 1 "Vault" caps & original red Nuka Cola & NEW Lucky 38
Lucky 38 (child) - NEW Lucky 38 caps to match various popular sets, both color and row profile
Nuka Cola Six Pack (child) - Row 3 Nuka Cola variety pack
Irradiated Travels (child) - Row 3 PC/GID "Vault" caps & others
Does that make sense?