I think you will not have a space problem even with 12 shirts. Let's get back to that later, though, and concentrate on the luggage question first.

Three bags aren't necessary. It is unlikely the 18" BR will need to be checked. It fulfills all regulations on the airlines you fly. The only thing I'm not sure off is the flight with JL. It looks like their weight limit is 10kg.
http://www.jal.co.jp/en/dom/service/bags/

Even if you needed to check it on that flight it wouldn't be so bad.

Skytrain, BR satchel and 235x are all too big. You don't need that much volume. They are also unwieldy to use as a day bag/briefcase and would thus require a third case. Ruled out.

BR 221 and 231x. Nice bags. But not a good briefcase format. Bye.

Medium/large size bookpack/backpack. If very soft structured not ideal for shirts even if you put them in a folder. Looks a bit sloppy. I always thinks Profs with backpacks are a bit strange. Hasta la vista.

That leaves us with the BB104x. Really nice bag. Totally big enough for what you want and need to transport. Use EC15 folder for shirts. Netbook and your diverse gadgets as well as files will find a good place in that bag. It looks good and professional, too. Will clamp onto 18 incher nicely.

Now that the bag problem is dealt with let's look at weight reduction again.

You will probably be staying in decent hotels, no? I mean places with a laundry service, or not? If that's the case, I'd take seven shirts. On Friday in PVG you give them 6 shirts to wash. Get them bag the same day or the next morning. They can fold them for you, too. Ready to pack.

You have 6 shirts packed and 1 that you wear for the trip to Florence. Save that for your arrival so you look proper. Departing China you can wear a polo shirt of t-shirt with a sweater or your hoodie. Be comfortable.

Once in Florence you still have 6 clean shirts to go. That should last until Thursday. T's and underwear can easily be washed in the sink.

So you see you can reduce the shirts from 10-12 to only 7, and do only a single laundry in Shanghai. It should be possible to get 6 shirts laundered and pressed in Shanghai overnight. And it shouldn't be too expensive.

If you were using non-iron shirts and you were willing to do some sink laundry you could reduce that to 5 shirts. That's what I'd do. I'd take 5 shirts and 5 sets of underwear. I might need to do laundry twice but it shouldn't be a problem because you stay in each place relatively long.

I also often wear a shirt twice. On the first day I will wear it with a t-shirt or undershirt under it. On the second day I will wear it with a pullover over it. If I didn't sweat horribly the first day they collar and cuffs will still be presentable peeking out from under a pullover on the second day. In April the weather won't be terribly hot in these places so you should get some good mileage out of your shirts.

Till