Want to update the paint on my outside deck. Do I need to sand it down, pressure wash it, prime it? Any thoughts on this? Was just going to pressure wash but I want to do it right the first time

Depends on whether or not you plan on putting some sort of water sealant on your deck as well.
Is sanding it and all of that the correct thing to do? Yes

Does it really need to be done? Meh

I use a solid deck stain (which is more, or less paint) on ours and never sand the previous coat off. I just pressure wash, let it dry and then stain. If I were going to go to the trouble of sanding, I would probably go with a semi transparent stain.

Checkout the Rustoleum restoration products...Restore4X is what I used and is holding up really well. Just follow the instructions.

Steps are like:
1 strip/scrub
2 wash
3 paint 2 coats.

Its actually a fun product to paint. It has almost a toothpaste like consistency.

For the record, a stain is what I would have preferred...I just didn't see myself being able to sand all surfaces of my deck, and I didn't want to replace.

I use a semi-transparent stain, but that may change next time. It is a pain in the ass to wash, sand, stain every 2 years.