problems in handling huge amount of status and comment
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Hi i am a newbie in web development.I am trying to develop a social networking site.At database design level feel some problem.Here is my problems..
I have a status table where attributes are

 - status_id(auto_increment)
 - user_id
 - status

My plan is when my home page load it will look for my friends from relation table(i have a relation table) and with the user_id from relation table it loads status(ordered by newest) from status table.
My question is  "is it a good plan?".I am thinking about it because this table can contain millions of rows(if i am lucky,but i need most efficient way) and if one user have 200 or 300 friend querying will work slowly?".Is it necessary to keep very old status in the table?please give me some advice about it?(This table will frequently insert status,so indexing may not be a good idea,what you say?)
I have also comment table where the attributes are..

 - user_id
 - friend_id(comment on whose status)
 - status_id(comment on which status)
 - comment

Here in no primary key.For this table question is same.
I am using mysql database and MyISAM as database engine.what about InnoDB?which engine will best for social networking?
please advice me.thanks in advance.....
  