My current batch of 6 pullets (2 EE, 1 OE, 1 Dominique, 1 BPR, 1 welsummer) is from Meyer Hatchery and they are all nice quality (but probably not show quality) birds. The sexing accuracy was 100% (thank goodness!).
Enjoy your new chicks! Isn't the waiting terrible!!! I've got chicks and...
It wouldn't hurt to get 6, as you could end up with 4 due to mortality or mis-sexed chicks.
I have (or have had) 3 of the breeds you listed: golden-laced wyandotte, black australorp and welsummer. The golden-laced wyandottes pretty much stopped laying around 22-24 months of age. This may...