Whether it is considered spam will deepend individually on the filters of those receiving the e-mail. Some will accept it, others will not. You have no controls whatsoever on that aspect.
Nothing you do in SMTP will harm the server. Either the server will refuse, or it will not.
I don't know that there is a constraint on the size of the BCC field. You will need to experiment, or hit the help file to find out. But you won't harm the server.