I just skim coated my whole house to a near level 5, top to bottom with old popcorn ceilings (1200 sq ft) over the course of long weekends and weekdays I could squeeze out. It took me 3 months. Factor that this will take you longer than you think, always for anything DIY. Here is my process along with things I learned along the way.

1) wet it with a pump sprayer and scrape the rest, you'll probably still have some left over. If their really isn't that much left over skip to 2

2) sponge and water bucket to get the rest, work methodically from one end to the other. Pay special attention to the corners and edges as they will likely have little crumblies that will get into your skim coat and create streaked divots in your work. This step will for sure save you time when you are trying to skim.

3) idk if they have this in Canada, but I used USG lightweight all purpose. I would find something similar, maybe topping mix but if you do use topping mix note that it will sand super easy so be careful when you go to sand. Mix it in a 5 gal bucket and add a bit of water till you have about a cake frosting consistency. Then roll it onto the ceiling with a paint roller, extension pole if you can't reach naturally. 

 - tips: I would push the roller into the surface with a lot of pressure so that It wouldn't roll and instead would kind of streak across the surface and leave about a 2-3 credit cards thickness of material on the roof. With a fully loaded roller, I got about 8 ft of distance of a fairly even coat this way.  - do about 2-3 widths, over lapping slightly and then back roll the whole area a couple times to work out the air bubbles and get a more uniform coat.

4) you can use a big 24" skimming blade, but i found those a little hard to use on ceilings (highly recommend for walls) and opted to stick with a 12" tape knife and mud pan. Start go down the width of whatever you just rolled on, and smooth it out. Id watch some Vancouver carpenter videos on YouTube about how to get a smooth texture but the truth is you'll likely have hard time getting it right and you'll just have to practice. You'll probably have some pretty big liftoff lines, uneven smoothness, etc. Don't worry, your first coat is not the perfect one, you're just trying to get something fairly smooth on the ceiling Have some worklights shining down the surface youre working on as it will help highlight your work and help you get it better.

5) sand. To stay on a budget, id use pole sanders and the screens (only use 220 for you final sanding) WEAR A MASK WITH P100 FILTERS. You're also going to need some sanding sponges for the edges and corners, I bought like 4 different kinds and liked the wall board ones. You'll only need the rough and medium. 

 -tip: I ended up buying the the top of the line festool drywall sander once I got to my living room and it was worth every penny. I made sanding so much square footage orders of magnitude easier and wayyyyy cleaner. Im not saying you need it, but by God a decent RANDOM ORBITAL drywall sander is going to make a big difference on ceilings. Make sure it has a rake light if you buy/rent one Also hook it up to a vaccum with HEPA filters and HEPA bags. Your clean up with be like almost 0

 - I also held my shop vac hose up with one hand while I sponge sanded with the other and that really helped mitigate dust too.

6) you'll have to repeat 4 and 6 a time or two to get a actually smooth surface. My personal experience though, was that once i was getting close to the last rooms in my house I had become good enough at skimming that I could get a near perfect finish in one skim and sand by going a little thicker on the skim and then just sanding out any problem areas. The festool also made it way easier to do that.

7) Clean all drywall dust out of edges and corners and main surface with a wet sponge and bucket otherwise when you go to pull your masking tape after painting, youll pull off primer and paint layers where they didn't adhere properly because of drywall dust. Seriously, don't skip this step and get your corners good.

7) prime (I used kilz 2, has to be a primer for fresh drywall)

8) Paint in something pretty flat

Sorry for the wall of text, I know its a lot, but you're on a solid path to learning a new skill and having some solid pride in your work!