How should i pay for my HDB? 50-50 cash & cpf? Supposing my spouse and i could pay off with cash alone, is this a wise move?

Always good to have flexibility to deploy cash whenever opportunity for better retuns arises. Do your sums when the time comes as the home loan rates then may derail whatever plan you determine today.

1) If you dun have a better use for the cash and want to save on bank / HDB loan interest + at the same time grow ur CPF (unused for monthly instalments) - yes wise move.

2) If you have plans to grow money e.g. put in SSB, Investments with guranteed interest over X years and the returns are higher than 1 - then won't seem to be a smart move.