should you always put a mill before any chopping when you 1 barack rush?i use to put it up when i got about 1500 wood left,is that good or does it slow down the rush too much?

If you are only 1 rax rushing you should be able to get your mill without slowing down your rush , AND without having to chop any wood first.

Once your mill is at about 250/600 you can start putting choppers onto wood. They will finish chopping just after the mill is done.
If you have a few choppers finishing just before the mill is done, stop 'em before they go into the hall. Then put them in once the mill is complete.

You should be able to do it like you say.