I have 2 polish, and 6 standard breeds. I love my polish, and they are very friendly. The only thing I would caution is that the rest of my flock picked on my polish really badly (especially the white crested black hen), to the point where I had to build a separate area for them. I wish I would have listened to the warnings and either gotten all polish or all standard breeds, not a mixed flock.
On the uphand, they are super cute, very friendly, and consistenly lay me an egg 5 out of 7 days.
I can't give any pointers on sexing.... it was hard for me to tell who was what until about 8 weeks old when their crests began to come in differently (my friend ordered polish with me and ended up with 2 roosters and 2 hens, where I had 2 hens).
As they grow and their crests poof out, you might need to trim their crest feathers so they can see better- seems to keep them friendly and prevent them from becoming spooky. Good luck! Enjoy them.