Generally, if you're lucky enough to have AC to start with, you want to step it down as much as possible while it is AC before converting it to DC. THis is because it is much easier to efficiently step down AC than DC (you just use a transformer, while to do the same thing you have to use switching converters which basically turn DC back into AC to be stepped down and then converted back into DC again).
You can just stick a current sensor to measure the DC...there isn't any real point to measure the AC and it's also more difficult. YOu can always work backwards with some math and find out approximately how much AC current you are drawing from your DC measurements.