will this INSERT profile work with my Mysql InnoDB oriented DB?

will this INSERT profile work with my Mysql InnoDB oriented DB?

I am wondering on the following subject (regarding INSERT on Mysql -
InnoDB tables).
I have a system that does among other system 2 things
promote a newsletter to users
mass emails to a certain type of users
now, the users will grow to 4k, and supposedly to 40k
When I'm mass emailing, I'm doing an INSERT for each user id in a WHILE
(which loops through all the users).
I have 2 questions :
Is this the best way to do it ?
When users reach 40K (40.000 users), will the mysql-server sustain this ?
thanks,