Ultra Wide Angle Lens?

I'm new to photography and I want an ultra wide angle lens mainly for night time cityscapes and occasionally landscape photography. I have a Nikon D5500 and want a 15-16mm FX equivalent, meaning I would want a 10 or 11mm lens. Since it would mostly be sunset, blue hour, and night time shots I would want one with a fast aperture. I don't want to spend too much on a lens, preferably under £500. I've looked into lenses and the one that ticks all my boxes is the Samyang 10mm f/2.8. The only downside to this is it can't have filters on it as the lens hood is built in.

Which is better for ultra wide angle shots, prime or zoom? I know that prime lenses are going to be sharper but is having the versatility of a zoom lens worth it or would just cropping it be better?

Then it come to the next question. Is there that much of a difference between f/2.8 and f/3.5 when it comes to lowlight shots? I'm looking at the Nikkor 10-24mm f/3.5-4.5G for the zoom range but was just wondering is it better to get a prime lens with a fixed aperture of f/2.8 for lowlight cityscape shots?

And are other brands like Sigma, Tokina, Tamron, good as well?
How do these compare with each other?

Samyang 10mm f/2.8
Tokina 11-16mm f/2.8 DXII
Tokina 11-20mm f/2.8 Pro
Sigma 10-20mm f/3.5
Tamron 10-24mm f/3.5-4.5
Nikkor 10-24mm f/3.5-4.5G

Ideally I would want a 10-20mm f/2.8 that can have polarizing filters.

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