If you intend to continue with the dreamfeed, then it doesn't matter if LO is waking. Just do the feed. In answer to your other questions, I don't think its a good idea to leave them in their crib, always pick them up. As far as quantity goes, its as much as they want of a normal sized feed.
When you start phasing it about 7 months, you bring it forward a little at a time at the same time decreasing the amount so that stops the habitual waking anyway.
HTH