Analog film photography and cameras

Let me first say I think there's some really cool shots!

Everyone recommended Portra 400, so that's what I got, but because it was always sunny and the film is so sensitive, I always had to keep the aperture closed almost all the way

So the EOS 300 can do 1/2000 ..was it really so bright you had to shoot at that speed and stop down completely??
Half of them don't look like it - especially not the last two you posted.

Anyways here's a few thoughs, maybe helpful -

..if you're absolutely certain it's going to be bright as fuck then yes, get 160 not 400.
160 isn't that much less sensitive than 400 though.
You can shoot 400 set at 200 or 100 (just hack the DX code) and some would argue you should do so, anyway. Remember it's not like with digital where your highlights blow out rather quickly - with colour negative film it's quite the opposite, you want to 'build up' details in the shadows.
You can get a camera body that can do 1/4000 or 1/8000.
You can also just focus not on the subject but quite a bit closer to the camera - if you are forced to stop down anyway and are shooting at top speed your subject will be sharp, and this will stop making the foreground look awkwardly unsharp and can helpa bit with making stuff that's far away razor sharp. Keep the 1/3 -2/3 rule in mind.

Good luck, enjoy, and keep up the good work!

There's a lot happening in the background

Find a better background? Not being sassy, something I know I need to work on in my stuff. Heres an example, see if you can spot the skater and board

Firstly, you deffinitely have some better shots than you’re giving yourself credit for, shooting skateboarding is notoriously difficult of course.

As others have mentioned you need to expose for your shadows and not the highlights with negative film (something you just have to get used to coming from digital, where the inverse is correct)

Otherwise I’d say just really try to think about other ways to try & create contrast within the image:

Composition - there’s nothing worse than a distracting background, unfortunately some spots will be difficult to shoot for this reason. You might find an angle which really compliments the trick but is just too messy for an image to really work. For instance with this shot you could have shot it like half a second later which would put the subject on a slightly cleaner background, as displayed on my highly accurate diagram below. (however you would also then not have the guy in the background perfectly positioned within the skaters legs which is a cool little detail. so it’s swings & roundabouts)

Otherwise a long lens + a flash would work too, but I do really much prefer skateboarding shot in natural light when possible.

Look at Rafael Gonzalez’ work if you’ve not done so already too, his work is beautiful!
Shooting black & white would be a good exercise too, that way you force yourself to think about how the composition & light creates contrast not the colours available in the scene.

Also note that overexposing the film will give you less contrasty files when scanned but you can pull a LOT of colour and contrast from Portra when you have a nicely exposed/flat scan.