K3 became obsolete so it’s not a viable option. Plus you do not want to be issued a K3 because it will not make your wife a PR upon entry like CR1/IR1 would. You’d have to adjust status and that’s more paperwork and more money and time.
You’re correct on those being your 2 options for no or minimal time apart, DCF being the superior option (if it’s granted).
Imho, I wouldn’t bank on that. You’re the petitioner and USC and free to leave Ireland for US at any time to start the job. It’s not really related to your wife in any way. USCIS does not care about separation as it’s a natural part of the process for most going through it.