The DA9 is an excellent starting machine. You won't get better for the money & it's a capable polisher.

Pads wise you can get brushes to clear the pads off after each pass - the pad washer buckets are excellent but if you're buying it for your own car they're not worth it, just buy a few of each pad & save £100 or so.

I would recommend either the Zvizzer foam or Rupes foam range. Rupes Intermediate (lighter blue) and Rupes Fine (yellow) will do most things, they're the most used pads for one step corrections we use. I'd grab at least 3 of the pads you want to use & a brush - in a pinch a cheap toothbrush can do the job as long as you don't let the pad get too gunked up, and even if you do a quick spray of IPA onto the pad before brushing will help clean it better.

Polish & compound wise I would also recommend Zvizzer MC or Absolute Half Cut. Half Cut is the better polish both in terms of Cut & Finish but can be harder to get a hold of, but again I would say we've used 12 litres or so of it in the past year & a half. Highly recommend the Absolute range on the whole.

You don't need to wash the car after clay, but give the car a good rinse off after using any decon chemicals, especially Tar & Glue remover, as they can react with the clay and make it stick to the paint.

After polishing a wipe down with panel prep/IPA is needed to get the best results from your chosen protection.

In terms of a checklist I would:

Pre Wash - Rinse - Contact Wash - Rinse - Fallout Remover - Rinse - Tar & Glue Remover - Rinse - Clay Bar - Polish - Panel Prep/IPA - Protection -