Seth Green wasn't about to come back when he was getting so much movie work. They really couldn't recast Oz with another actor because American fans just link the actor and charcter so closely. Now if you ask what might have happened if Seth Green was out of work and Joss was in a funny mood...I think it would have been a riot. He would have hung with Lorne. Been a possible boyfriend for Fred-might even have called her Winifred because he liked the sound.
Eh?
First and foremost, Seth Green was doing a fair bit of TV work. He wouldn't have to come in as a full on cast member to have a real presense for the year. Heck 10 episodes and he'd he significant enough while at the same time to pursue his movies.
Also, I have to take issue with your 'American Fans' thing about Oz being recast. Oz being recast would have an effect on the entire fanbase around the world, not just the Americans. I know i'd not be completely happy if any of the characters came back but had a different Actor in the lead. HAVING said that, give me a character with a different actor in a role over no show anyday IF the actor replacing is good enough. It wouldn't have been the first time that this sort of thing happens in a TV show.
Now, onto your comments about the characters.
Why wouldn't Oz have been in favour of the move to W&H?
None of the characters should have been OK with that idea, specifically Wesley in my opinion, yet they did it. Why?
Well two reasons fundamentally.
1) They felt that they had resources that they could use to 'fight the good fight' on a grander scale
2) Because Angel said so and each one of the gang trusted Angel.
Oz would have gone with. He may or may not have sounded caution but he would have gone.
Also, i'm not seeing your linking either.
I see there is a connection between Lorne and Oz musically, however I don't feel that is strong enough to say that Oz would 'hung' with him.
I mean lets be honest here, you wouldn't expect to see Elton John out partying with the Lead singer from the Kaiser Chiefs.
AND again, not exactly seeing the 'Fred' connection either.
Oz liked Willow. Willow was intelligent.
Is that how you got that?
Pretty safe to assume thats your main connection, that or the basic He's a he, she's a she and he wouldn't be with Cordelia because thats Angels girl.
Well see my problem would be that Cordelia would be his better suited partner and i'll tell you for why.
They have a history. They have a mutual respect. They have that Cool guy - Hott Chick sorta thing. They'd be like Pete Doherty and Kate Moss.
Fred on the other hand had her hands full as it were. She had both Gunn and Wesley who, in my opinion, are absolute musts for that show to be what it is. With Buffy you can imagine certain characters could have been taken out of the show with little effect, Gunn and Wesley, well they are core elements of its strength and growth away from its Sister show.