think when collect key we already pay first installment. during my first apptment they gave me a finanical plan (I had my HLE then) when the letter to collect key comes, there is a workout financal plan without your CPF yet. When you go for the appointment they will work it out and show to you.(if i rem correctly)
HDB Loan they will clear everything of the OA account. during collecting key, think the first installment is also deducted.
I saw this finanical planning from HDB Link
http://www.hdb.gov.sg/fi10/fi10201p.nsf/WP...w?OpenDocument#
hope the above is useful