.How soon can I actually get my mortgage approved & signed off?
You can get the apprval any time you want but depending on the institution it might only be valid for 6 months/1 year,
(2) Can I agree the mortgage now & avail of potentially better int rates & first year deals as of today?
Unfortunately not, you get the interest rate that's in place when you draw down. We bought a house off plans last April and have seen interest rates rise and rise but because we're not ready to draw down we just have to accept that whatever the rate is when we're ready is what we're stuck with.