I think using that Bock yeast you'd be more likely to hit your apparent attenuation number if you increased the beta conversion a little, it should still be plenty malty. It shouldn't be sweet either way, as long as you get a good full attenuation (for the given wort fermentability) the mash temps/times won't really make it sweet. Your temps are classic Hochkurz temps and I wouldn't change the 160* F rest (I often shoot for 161* F there and for a similar time).
For me, the hardest part of your mash schedule would be to get the first decoction converted and boiled in that 20 minutes. Your 145* F (or whatever you choose) rest may end up being as long as it takes to finish boiling the decoction. I don't think you're going to get much higher than 76% AA (which is your target) with that yeast unless you mash for really high attenuation.
If you're concerned with the beta rest going too long you can always lower the beta rest temp a little to slow it down a bit. Conversely you can increase the beta rest temp a tad (to 147*-149* F) and it will work a little faster. Everyone's system is a little different, I tend to get high attenuation for a given mash and I'd prob rest at that beta temp for 30-40 minutes, then another 30-40 at 161* F, then mash-out.