A word of warning: Horstman House is ski-in but it's definitely not ski-out! Shouldn't be a problem since it has its own shuttle.
1. Rental tips: Renting from the mountain itself is expensive (but there is a 20% discount if you have an Epic pass) BUT very convenient - you can check it in for free overnight & I think you can have it sent to Whistler if you rented on Blackcomb etc. Best to call customer service and confirm though.
Black Tie will bring skis to your condo to fit, which is cushy.
Spicy is the best value & there is a shop at Blackcomb base.
All will let you pickup from ~3pm the after before your rental official starts.
2. The reservation system for mountain restaurants is no longer in effect this year. You should be okay since it's midweek but just for reference: Chic Pea or Pikas (downstairs part of Roundhouse) are the best options on Whistler side, Glacier Creek is better than Rendezvous over on Blackcomb.
2b: I am not sure the guided tours still exist: the consensus in the subreddit is that Vail cancelled the program (no-one has seen signs for it on the mountain, although I did ski past a group just after 11am last Weds outside the Roundhouse that *might* have been the hosted groups.)
3. Check the freezing level on the weather report: this will help prepare you for the snow conditions.
https://www.whistlerblackcomb.com/the-mountain/mountain-conditions/snow-and-weather-report.aspx.
e.g for Monday 20th, the freezing level is at 1200m. With overnight temps of -6C, that means that just below mid-station the snow may have melted during the previous day & refrozen overnight, so it will be icy in the morning (not a problem coming from Ontario!) granular mid-day and sticky or even slushy in the afternoon.
Most of the time the challenge isn't skiing in powder, it's skiing in the aftermath of several thousand people skiing through 10cm of heavy, wettish snow, so even groomed runs have many sections that are ~halfway to forming moguls.
3b. Apropos of weather: Do not freak out when you are riding the gondola up & you pass through clouds. Quite often it will be perfectly clear up top with a band of fog around the middle - on those days, the high alpine can be really enjoyable. Just keep an eye on the clouds moving in because it's unnerving to be in the Alpine when it's totally foggy. Be prepared to ski with poles dragging on the ground to help with your orientation if you get enveloped in fog in the alpine. Otherwise stick to runs with trees on either side for better vis/definition.
4. If you are really nervous about the difficulty of the mountain, start on Whistler instead of Blackcomb. Mid-week the Whistler gondola queue should be fine, otherwise take the Blackcomb gondola up & then Peak to Peak over. To add to Christy's excellent advice:
a) Warm up with laps of the Emerald Chair. Upper & Lower Whiskey Jack and/or Ego Bowl are the easiest. Marmot has one short steepish section that gets mogulled up very quickly. The progression is then to Green Acres, which has been relabelled as a blue this year (but I heard instructors referring to it as a turquoise/teal as it's mostly green in nature BUT has a short pitch that again, gets tons of moguls.)
I would then do Red chair - lots of nice blues on that one. Then I would progress to Harmony, *if* it's a clear day, Harmony Ridge being particularly lovely (but see my comments about fog in the high alpine). Note that Symphony & Harmony chairs close early at 2:30 because it's a bit of a trek to get back to the main area in Whistler. They also seem to have the worst lines - on Tues last week and I had zero lines at Emerald and 20min wait at Harmony
The Saddle was upgraded to black this year, which feels right as it was always steeper than Raven (a short groomed black off Garbanzo) - apparently the receding glacier has made it even steeper. There's a convex roll at the top which is pretty unnerving as you can't see over the edge.
On Blackcomb, the progression is: Easy Out (Catskinner chair) and then straight to blue runs, with Wishbone being the teaching zone blue that has more ski patrol slow zones. There *are* other green runs but they are cattracks & not much fun. Of course, what I call icy you might find totally okay, in which case there is a green run all the way from the top of 7th Heaven that might be fun in good weather.
My caveats on the progression that Cygnet listed above is that with the decline in quality of piste grooming under Vail, what are listed as lower intermediate runs off Excelerator are highly dependent on freezing level and/or the amount of snow that has fallen. Too often it's piles of mushy crud with skied off hardpack between. Note that the guide was written before the Blackcomb gondola opened, so Wizard = lower Blackcomb gondola (Grub Stake is a particularly mellow blue - I like to ski this one as the home run at the end of the day). The top of ZigZag is nice but the bottom half is meh.
Wishbone is the teaching zone blue - there's a weird pitch right in the middle before Cruiser splits off that is always cruddy with nascent moguls forming, but otherwise okay. Jersey Cream is probably the most reliable chair in terms of quality of snow & length of queue for the chair (it starts off as alpine & the entry is a little icy/mogully but quickly flattens out). The blues in Crystal are the nicest, even if they are listed as being the most difficult (some of the entrances have been resculpted to be easier than when the book was originally written.) Ridge Runner is always really well groomed, Rock'n'Roll to Backstage Pass is great when groomed, but that's only M/W/F, although the first pitch is pretty steep. The blues in 7th are definitely the most difficult - I always have a brief moment of freaking out at the start.
Hope this long ramble is helpful - feel free to PM me with any specific questions!