There is a size limit now so it needs to be around 1.5 mb in size. The max resolution is 300 x whatever.

I suggest loading your video into after effects, rendering a new avi from it and resize the output file to 300x169. Then create a new composition and drop your 300x169 avi onto the comp and cut your time line down to around 10 seconds. At that point you click on File, export, Adobe Flash player(swf), name the file and click save. The swf settings box will pop up , choose jpeg quality 5, check the loop continuously box and click OK.

Your swf will create. Check the file size and if your around 1.5mb, your golden. If it's over 1.75, delete it, change your jpeg quality to 4 and create another one. Check the file size and if your around 1.5mb, your done. If not, try again.

You can also shorten the clip to 5 seconds to lower the file size.

Hope this helps. If you can't figure it out from these directions, let me know and I'll try to find time to create a training video this weekend.

You can edit your discription without it going back into moderation but I'm not sure about the rest. 

I'm at Master rank so it's been a while since my uploads went through moderation. Maybe someone that knowns those answers will comment.

When updating you only need to upload what you are changing.

It's been hit and miss for me with previews for the same reason as you describe.

If it helps, I've had the best luck with FireFox.