Yes, I have exactly the same radiator and it fitted into this case without any problems. It even looks very good, as the inscription on the radiator grille is very legible through the glass. You should have no problems fitting this CPU cooler into the Spec Alpha. Kind regards!

Front 2x120mm

I think there is no power supply included, otherwise a power rating would be listed. According to the specifications, the maximum length of the power supply unit is 190 mm.

it should be possible, the space is there, but i have never tried it myself.

Power cables come with the power supply unit, data cables with the mainboard. All cables for the front panel are normally supplied with the case. For example, for the start button, front USB and jack connections, etc.

yes

From the specifications: Number of fans 3 x Number of fan slots 5 x

In my case, they were normal cross-slits.

Tends to be the one on the back of the enclosure. I could not find out from the Seidon whether it is possible to mount two 120mm fans with the enclosed screws. However, the fan from the back could be attached to the lower part of the front.

According to the product specifications, it will last a long time: the Corsair H100i v2 (5.50cm) is 55mm high and in the case the CPU cooler may be up to 156mm high.

As you can see from the specifications under "Front" and "Back", the maximum size is 240mm and 120mm respectively.