I have 6 helix piercings, and these are my answers based on my own experiences:
Is the aftercare tricky, wondering if I need to clean it twice a day and avoid swimming?
No, it's not tricky at all. You do need to clean your ears twice a day, yes, but it's easy to do. And, I would avoid swimming for a short while.
How long is it painful to side sleep?
For a fair amount of time, in my case. I actually couldn't sleep on my side unless I had some kind of "buffer" that meant that my pierced area didn't get pressed against the pillow. I quickly became a back sleeper!
What’s the timescale to have it replaced with a shorter pole?
My healing was really slow, so it took months. My helix piercings healed the quickest, though, while my conch piercings healed the slowest.
How long until I can swap to a different earring?
Again, I personally waited for a long time (as in a couple of years, if not more), but that's not necessarily what works for someone else. But as I said, my healing was really slow. Maybe because I got too many piercings all at once.
What’s the recommended metal?
There are many metals to choose from, it just depends on your preference and budget. I have tried titanium, steel, solid silver and solid gold. I prefer solid gold, but the most durable metal would probably be titanium or steel.