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Command
nslookup seed.bitcoin.sipa.be
gives a list of 40 nodes.
1) Does Bitcoin wallet take all nodes from that list?
or
2) Does Bitcoin wallet behave like normal application that resolves seed.bitcoin.sipa.be and take only one IP address to connect.
seed.bitcoin.sipa.be and the other DNS seeders listed here will return a list of IP addresses when given a DNS query. Bitcoin Core then takes all of those IP addresses and adds them to its internal address manager. It will then attempt connecting to the addresses stored in its address manager which, after the first start, will consist of more than just the nodes returned by the DNS seeders.
addnode=seed.xxxxxx.com or type addnode seed.xxxxxx.com add does Bitcoin Core add all IP addresses or just one IP address to it's address manager?
addnode will add the one node that you enter to the address manager and then attempt to connect to it. There are no "all IP addresses" for it to even add; you are only giving it one IP address.
The bitcoin client will first try to scan for previous known IPs, once that fails, it will indeed fall back on DNS seeds.
It will resolve seed.bitcoin.sipa.be to a list of IP adresses and it will pick one of them.
