My First NAS home made !

Fractal Node 304, good case ... but why the Kaby Lake T-Version? i5-7400 would have been a better choice.

In Node 304 fits even a Thermaltake Macho tower cooler. I have a Xeon E3-1230 V5 in my Node, its a 80 Watts CPU. (FreeNAS system, my second NAS is a AMD 5350 with OMV)

That is an erroneous belief. i5-7400 and i5-7400T use the same energy when idle and your NAS will be basicly idle 90% of the time. The T-Version is for compact cases where the 65 Watts of the i5-7400 can not be cooled. Therefore you lack power reserves. Since the the i5-7400T takes more time to finish a scheduled job it will consume less power than the i5-7400, but for a longer time. Its an integral, the amount of energy is the same, but the peak is lower, just for the reason of cooling. technikaffe.de issued a review of a T and a Non-T-Processor. It's a translate from German. Check TDP article for reference as well.

T-Version = More money for less power. Only reasonable when cooling capacities are limited.

Thats right, the i5-7400T is still a good processor. Even much less powerful CPUs can handle OMV with ease.