I am just about to start reloading .223 and I got to thinking about all the steps.

After resizing comes trimming if necessary, right?

But if I'm using a turret or other multi-stage press how do I know if the resized brass is too long before it proceeds to the next stage?

Frist digest this......
You will never progressively load bottleneck cartridges!

Progressive reloading of bottleneck cartridges is some along this path.....

Clean not necessarily polish case to remove debris and detect defects
Lube Cases inside case neck and body.
Size Cases
Remove from press for further inspection and case prep:
Remove lube from cases by polishing
Measure cases and trim as needed
Chamber and deburr case mouth
Remove primer pocket crimp if need be
Uniform primer pocket if desired
Debur flash hole if desired

Now with prepped brass.....
you can progressively load the brass

That's pretty much the jist of it.

In station one of my 550, all I have is a universal decapping die to knock out any tumbling media that may be stuck in the flash hole.

Dont forget about having to hand prime if you are using a L&L AP

Got it. Thanks. I see where I went off the rails now.

Huh?  You might want to hand prime, but it isn't required.

My setup: deprime and wet tumble with stainless steel pins (the brass looks better than new)
Lightly lube the cases (spray) and fill the case feeder
Size with automated case feeding
Trim with Giraud trimmer (every case; if it isn't too long it won't be touched)
Tumble in corn cob to remove lube then put up until needed
Start a loading project by setting up the LnL for the right caliber and powder charge
Pour the sized cases in the case feeder
Prime on station 1.5, powder drop on 2, Powder Cop die on 3, bullet seater on 4, crimp (if needed) on 5.
If no crimp is desired, I can put the bullet feeder on 4 and seat on 5, greatly speeding my process.

Keep the press, and especially the primer feed track and surrounding parts SCRUPULOUSLY CLEAN and you won't have problems.

Not me.  I prime on press with the LNLAP.  The primer shuttle area does have to be kept clean.  Any spilled powder here will make priming misery.