Finish scraping the rest of the paint, and it wouldn't hurt to sand it some either. Yes, you'll want to use an exterior all-weather primer before using paint. Taking the time to do it right the first time will save you headaches in the long run.

Finish scraping all the loose paint. Don't use a pressure washer unless you have a few weeks of dry weather to let it dry properly. Use bleach/water 50/50 to kill any mold/mildew. When everything is DRY use an exterior primer. The alkyd ones are best but they are making very good latex one these days. After a good primer coat finish with two coats of high quality latex exterior paint.

Rent a pressure washer. If you are down to bare wood for large sections, priming is a good idea.

We have an open front porch on our house. It has one layer of peeling paint and the porch also has mold/dirt/pollen, the usual outside wood elements on it.

I want to repaint everything, the floor grey and everything else white.

I've taken a hose with nozzle attachment and washed down the floor.

What else should I do to get the porch ready to paint? Also, should I use a primer before I paint? A lot of the porch is down to the bare wood.

Thanks.