140 mm long PSU for Antec ISK 600

[quest_for_silence]

Could you please explain in plain words your sentence? I really don't have a clue on what are you talking about...

A not-PWM header can safely supply up to 0.8A without blowing (some even 1.0A peak, but I won't try): so when you connect more than a fan to any single mobo header, you should check how much current all those fans will draw, and that current is written on any fan hub label.
With a PWM header you can use a PWM splitter sporting a Molex 4LP power supply connector to feed all the fans, so you have not to bother about their current ratings.

Given CS450M connectivity options, which type could suit me better? Maybe this one? I have to connect an SSD and a HDD too.

Theoretically a two SATA connector to one 6+2 pin PCIE connector adapter would be better because you will have one less big/stiff PSU cable inside to route, but at the same time you won't stress one SATA connector only on the PSU SATA cable.
But there's a small chance that routing issue may put the available SATA connectors in some troubled position to reach with the adapter, so take my advice with a pinch of salt.

As noob as I am, sure I'll discover too late.

That's life: we call experience what we know one second after we needed it.

[morganITA]

A not-PWM header can safely supply up to 0.8A without blowing (some even 1.0A peak, but I won't try): so when you connect more than a fan to any single mobo header, you should check how much current all those fans will draw, and that current is written on any fan hub label. With a PWM header you can use a PWM splitter sporting a Molex 4LP power supply connector to feed all the fans, so you have not to bother about their current ratings.

The only info about R2 92mm I found report 0.48 W +/- 15% power for each fan so the total amount should be ~0,092A @ 12V (rounded up by excess). How this could be an issue for mobo header if its maximum is 0.8A? Or maybe should I just go back to the high school?
EDIT: just found the answer to this question on a Node 304 forum:

Ran all 3 fans off my Asus P8z77-i deluxe mobo no issues(actually still do), that header is rated for 1A(12W), more than enough for a 140 and 2x92 in most cases.

Theoretically a two SATA connector to one 6+2 pin PCIE connector adapter would be better because you will have one less big/stiff PSU cable inside to route, but at the same time you won't stress one SATA connector only on the PSU SATA cable.
But there's a small chance that routing issue may put the available SATA connectors in some troubled position to reach with the adapter, so take my advice with a pinch of salt

That's life: we call experience what we know one second after we needed it.

And this is a perfect example!

And now the sad part: the total for this new config is almost 170€ higher(!) than my 1st estimate... The only way to save some cash is to renounce to the biggest upgrade for me: the SSD! I'll probably wait until windows 10 is out and so update my os too, all together. After all, I lived well without it until now so few months of waiting are definitely affordable in exchange of some (I hope) quiet.

[quest_for_silence]

And now the sad part: the total for this new config is almost 170€ higher(!) than my 1st estimate... The only way to save some cash is to renounce to the biggest upgrade for me: the SSD!

Check whether an ASRock or Gigabyte board may give you some substantial saving, and/or look for a caching solution, like the Sandisk Ready Cache (or a used SSD).

[morganITA]

Check whether an ASRock or Gigabyte board may give you some substantial saving, and/or look for a caching solution, like the Sandisk Ready Cache (or a used SSD).

Evaluated all mobos with same features but the difference with the Asus are around 5-12€, with also the chance to discover some unreported clearance incompatibility or fan government issue, I don't think I want to risk for such money... I also received a pm from Abula which confirm nothing but good about Asus fan controller+bios+software. About the ssd, I take the decision to delay, silence appear to me most important than performances in this moment.
And now the other great challenge: find the spare time to order and actually set up everything. This will be another though part, it could take weeks...
I'm really glad I found all your good advices, I don't know what messy result I'd get without you, thanks! I'll surely keep this thread updated with all my further steps!

[quest_for_silence]

About the ssd, I take the decision to delay, silence appear to me most important than performances in this moment.

As said, in order to gain lots of the SSDs advantages with a relatively few money, that one may deliver.
I often (three times, to be fair) used caching solutions from OCZ (same of Corsair and Crucial) and Sandisk, and the difference in "snappiness" IMO was just huge (with reference to an HDD-only solutions).

I'll surely keep this thread updated with all my further steps!

We're looking for that!