1- Not without a budget and currency, no.

2- Be Quiet Pure Wings 2 are great fans, I love mine in my H440. Do not go for Corsair AF/SP fans with LEDs, I know they're the go to but they suck, which is why I got rid of mine. Plus, LEDs on fans are useless IMO, just get some nice LED strips or an NZXT Hue+ or something. If you really want, their should be new fans coming from a bunch of companies with RGB LEDs this year.

3- Aftermarket, always. Especially with the weird derping going on with "Founders Edition" cards these days. Blower style coolers only help in very small cases because they take the heat from the case and blow it out the back, this makes pretty much everything OTHER than your GPU cooler. Aftermarket GPUs with fans, blow the hot air around the case and let your case fans deal with it, so your GPU stays cooler(often significantly cooler), but your other components have to deal with the heat, which just isn't an issue in ATX, or even mATX cases. Heck, even mITX cases like the Define Nano S and Enthoo Evolv ITX are better with aftermarket GPUs IMO.

4- Depends. Almost always, yes, though sometimes you may have to buy one or two small extra things.

5- Neither? I don't know. No one can answer this considering you haven't told us the differences between them, other than the heatsink used which is totally irrelevant. All RAM comes from like 3 different companies that produce it, then the people at Kingston/Corsair etc throw their own heatsink on it, so brand makes no difference when it comes to RAM. Just buy whatever is compatible, cheapest, and looks good to you.

It'd be a lot easier if you told us what components you already have, what you need, and what your budget/currency is.

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Thats what I'm looking at getting, I already have the CPU, Monitor, Storage and network card that I've got from my other PC, is there anything you'd improve? Nothing too expensive but if something costs 20-30 quid more then I don't mind

Alright, that helps.

GTX 1070 is super overkill for 1080p. It's also way over-priced for a 70 series GPU from NVidia, and IMO, you'd be better waiting 10 days for an RX 480. That PSU, the CX600, is terrible. Don't touch it. As I said, those fans aren't good. You also don't need a bunch of fans, included case fans are more than enough most of the time.

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Better mouse. Better, mechanical keyboard. XFire support so you can buy an 8GB 480 when they release in around 10 days, and have the option to add a 2nd 480 at any point. 2 x RX 480s supposedly out-perform a single GTX 1080 for around half the price. Cheaper case but still nice, the Enthoo Pro M is another good alternative but I thought you might appreciate the built in LEDs with the Eclipse P400S. The H440 is still a great case though if you want to go for that, you can see my review of it here;
https://www.thetechgame.com/Forums/t=5249783/hardware-reviews/start=14.html

Significantly better quality PSU. Better and quieter fans. Use 2 x140mm in the front as intake and that one 120mm in the rear as exhaust. I also included a nice monitor upgrade since even the 480 is going to be overkill for 1080p IMO, and your current 1080p monitor isn't very good quality anyway so an upgrade definitely wouldn't go amiss. I would advise upgrading your CPU cooler in the future at some point if you're running the stock cooler, I'd also advise adding another SSD, and maybe HDD. 620GB storage is very minimal these days.