Yes, the increase in brake pedal travel is completely gone now. That was the new pads still needing to glaze a bit.
If I would guess the added spacer could be as thin as 3,5mm. The original caliper carriers are ment for a 338mm disc (the z4m disc is 345mm (+7mm :2=3,5mm)).
I don't know if the 338mm (1 series) disc would fit (offset etc).
It's too bad that there's no data on the bmw performance (/m) discs. Normal discs are also made by brembo etc and they have data on their site, but but that's not the case for the performance /m discs.
The rear still is a matter of making your own like I did. I don't think I've seen a manufacturer making a rear bbk for a non m Z4.
Then again on a z4m you can't have the bmw performance calipers I think
(unless you make them fit of course)
My rear setup still works fine. A few weeks ago I disassembeled my complete rear axle (I've replaced all 19 bushes for poly) so I had a good look. 1 e brake pad I welded again because it bent a bit during desassembly.
Carefully tig welding (nice small weld) stops the need to grind off the weld on the pad for the spring to fit. (grinding the weld weakens the weld obviously)
Too bad that ECS is still incresing the sales price of the front bbk (I paid more than $500 less 1,5 years ago than the current price), but thats how things go.