Looks nice, why don't you put a ball valve and a drain after exp tank for when it goes bad you don't have to drain the whole system to Change it?
With flow checks and isolation flanges normally I would disagree. In this boilers case I would say good idea since what is involved in purging the radiant zones. Didn't design the piping on this job though. On a normal system I never have any issues just dropping the pressure and isolating the supply to do an expansion tank.
You can't verify pressure in exp tank without isolating it either. I'm not trying to sound like a old nag lol but it makes life easy.
Yeah I guess that is one good bonus.