Which products do you already use? Do you double cleanse in the evenings? I'd try that first and then I'd try the Paula's choice. So an oil based cleanser first to remove SPF and make up, then a cream or lotion cleanser to remove any residue and clean your skin. Simple is meant to be good for an oil based and it's only a couple of quid. Give your skin 6-8 weeks of that and see if it helps with the cheeks and blackheads.
I wouldn't spend a heap of money on the ordinary until I knew exactly what I wanted. The individual prices are cheap enough but it soon adds up. Toy can't start them all at once in any case as if anything causes a reaction you won't know which one it is.
I have seen lots of people reporting positive results with the niacinamide but I've also seen loads of people saying it caused their skin to break out.
Your basic routine should be cleanse, hydrate/moisturise (superdrug do a hydrating serum if you think you need one) and SPF of 30. In the evening, double cleanse, hydrate/oil/moisturise.
It depends on what you think your skin needs regarding hydration or moisture. Some people find their SPF is moisturising enough by itself. Or you don't need a hydrating serum because your skin isn't dehydrated. Or you don't need an oil because your skin isn't dry.
Paula's choice is also Salicylic Acid. £8 for same size as the Ordinary. I suspect it's better (disclaimer I haven't tried either of them).
m.lookfantastic.com/paula-s-choice-skin-perfecting-2-bha-liquid-exfoliant-trial-size-30ml/11174179.html?settingsSaved=Y&shippingcountry=IE&switchcurrency=GBP
CeraVe face moisturizer (not the one with the SPF) contains niacinamide and might be helpful.
I just wouldn't buy all that The Ordinary stuff and try it all at once. You won't have any idea what's helping or breaking you out.
I think the Buffet might have had a positive effect on my skin but it also caused any hair on my face to look lusher. Great for eyelashes, not so much for peach fuzz.
It's really all about trying to get to know your skin!