My deck is 20x20 and I like that it is large enough for a party. We have white
vinyl railing around it and I love how it looks. I always thought I would feel like I was in a playpen but I was totally wrong. The white gives it such a clean, finished look.
If you need privacy from neighbors, why not incorporate a privacy fence into your deck design?
If you need privacy from above, a pergola or roof would definitely help.
I highly recommend an actual roof over your hot tub. My parents have a hot tub at the cabin on their farm and they love to use it during periods of light rain or snow. It wouldn't be the same if it were raining
on you.
You could do a skylight if you're interested in a view of the stars. My ILs have a retractable awning and it's great for the sun but I'm really not sure how it stands up to rain.
Speaking of privacy, my parents have neighbors near their cabin who like to use a telescope. We cannot confirm the telescope is pointed at my parents' hot tub but when my parents went for dinner, they moved the telescope suddenly (& in a suspicious manner) so that my parents didn't see exactly where it was pointed. They are sort of goofy and are in the 80's so my mom says it doesn't bother her but they've planted some shrubs in between since then.