Do you consider it Biblically ok for a church to not have a deacon?
I would say that it's okay, but not the ideal. I mean that in a similar way to what Paul says about it being good for a man not to marry. There's nothing technically wrong with it, but it is not the ideal. Growing up (well age 7 on) in the OPC the church we were in was small, so the need for deacons wasn't there like it is in the church I'm in now. Eventually it got to be too much for the elders and so Deacons were nominated and then ordained... much like what we see with the first Deacons in Acts.
What do you mean by a church can function without a deacon but not an elder?
In a presbyterian form of government there needs to be a plurality of elders. See
The Apostolic Church: Which is it? by Thomos Witherow. Short yet excellent book that explains presbyterianism. That can address your eldership questions in the immediately-above post.
