you'll have to wait for the start of the next month. it'll show up in the Fitness app on your iPhone.
they're 'personalized' based on your past activity, but generally pretty useless. used to be that they'd give you absolutely insane challenges that weren't reasonable if you cared at all about rest, recovery and injury pervention, but since watchOS 9.0 or so, they've seem to have swung the other way and have always been incredibly easy to accomplish for me.
yeah, you'll get the occasional erroneous reading
with the stock app, yes. with a third party app like Workoutdoors, you can have a much larger range of metrics to choose from and display.
i would keep in mind, though, that optical heart-rate sensors do struggle with getting readings while swimming in water and Apple notes that you may not get HR readings for swimming workouts.
you're losing the always on display and ECG, but also getting a significantly newer SoC and (likely) more future watchOS updates
rest and recovery aren't concepts apple have ever heard of.
but yeah, you can turn off the nagging reminders
my belief is that it's a watch and a basic necessity of such a thing is an always-on display
it doesn't measure vo2max at all. it does need GPS data for an eligible activity (>20 minute outdoor runs/walks/hikes) because the estimate it'll spit out is reliant on some data like distance, pace and elevation that is derived from GPS (and other data points, namely heart-rate). none of that stuff requires a data connection
the watch is only going to spit out vo2max estimates for >20 minute outdoor walks/runs/hikes that meet the eligibility requirements it wants (namely, relatively flat elevation during those activities), so i'm not sure how relevant any estimates you're getting are going to be if you're not doing a lot of those activities.
the watch is, of course, incapable of giving you an actual vo2max measurement anyway, since it can't measure oxygen consumption. and even properly measured in a lab with an oxygen mask, it's not a particularly useful performance metric.
i wish i held off... maybe give it until 10.2. there's not exactly anything that you're missing out on as far as features anyway
yeah, it'll want a GPS track. the primary ways it spits out a vo2max estimate is by looking at your heart-rate and pace, so it needs distance information. it also wants to know the elevation data so it knows only to spit out an estimate if the run was done on relatively flat ground (it's an estimate because the watch isn't actually capable of measuring vo2max since it can't measure your oxygen consumption).
the two main things for me would be the battery life and multi-band GPS, though really, Apple has no excuse for those things not being far better than they are on the Series 9 currently.
i don't know, but Spotify will let you (can also control it from the Watch on tons of other devices)