1) as the default is no ipv6 unicast-routing then the router won't send any RA and won't reply to any RS.
Once you have enabled ipv6 routing then it send RAs and reply to RS unless you configure ipv6 nd suppress-ra on the interface
I don't know for question 2 as I've never used nor labbed the prefix delegation feature yet.
"no ipv6 nd suppress-ra" command is needed only for when I use ipv6 nd suppress-ra. Is it true?
I wonder that if I configure RA message with MTU and some others paremeters, and than if I restart Cisco and enable routing again, RA message includes same parameters as before resart? Or are there default parameters at system statrup?