Potential pitfalls with TLC5940, 4N35 and N-MOSFET

Hi all.

I'm planning to implement room lighting with three 12V 6A+ led-strips.

Also I want to use separate power supplies for each of those strips.

My initial idea is use Nano with TLC5940, which might be bit overkill, but there is also reasons for that. And for that Nano and TLC5940 will be driven with 'some' 5v supply.

After that TLC should be 4N35 for every channel, which also conveniently inverts that signal, which will drive that N-MOSFET.

There would be four 'sites'. Arduino + TLC in one and three powers with mosfet.

And why I want to make this so hard?

1) TLC have more bits in pwn and it helps with high-power led-strips, at least in low duty cycle end.

2) Ofc I could buy 20A power, but three 6A+ powers are imo better solution. Why? 2.1) Shorter 12V-wires, distance is at least 10 metres. 2.2) No fans. 2.3) Already double insulation with plastic casing. 2.4) That big supply would be single point of failure. 2.5) 230V transfers more efficiently than 12V, with thinner wires.

So, suggestions?

Is that 4N35 fast enough for that pwm?

Should that 4N35 near that TLC or those MOSFETs? Distance will be many meters and I try to use as thin wires as possible.

Something else?

Ofc I could use radio-transceivers and three Nanos, but that low-bit pwm would still be problem. Transition between level to level is too high and it flickers. It isn't problem with lower power leds...

My main concern is, how I can ensure, that this mosfet is in saturated state, as much as possible.

I think, that there is rising time in that opto's transistor, in which time that mosfet is in triode/linear region and resistance is higher, which adds heat.