Hello brothers
I'm trying to build a solar system but I'm confused about some of the technical specifications.
I bought an inverter Axpert iii 4kw and these are its technical specifications as shown in the pictures:

 

And i want to buy solar panels from Jinko Solar. These are the specifications of panels as shown in the picture:

 

When looking at the MPPT voltage range you find the voltage range is 120~450VDC and logically connecting 3 panels will give about 127vdc and this number falls within the required range, But if you take a look into the inverter catalog You will find the star-up voltage of MPPT is 150VDC and this number is greater than 127V so logically if you add a fourth panel, you will get 169V from the four panels, and this number falls within MPPT Voltage range 120~450VDC also greater than the star-up voltage 150VDC, Well it seems everything is perfect.
Oh no wait.
What is this thing called "Nominal operating voltage:320VDC?!"
Can someone explain what this means?!
Is it necessary for the panels voltage to reach this number?!
Or is this the ideal voltage that the MPPT works with and it can work at lower voltages without problems.?!

Finally, I have some questions:
The first question: What is the minimum number of panels that can be installed and the MPPT can work without problems?!
The second question: What is the ideal number of panels that prefer a combination?!
The third question:If the maximum number of panels that I can provide is 4 or 5 panels,Is it preferable to replace this 4KW  inverter with another 3KW inverter that has "Nominal operating voltage:240VDC" Or there will be no difference?

Thank you all

Minimum would be 4 panels, most ideal would be 8.

For nominal operating of 320VDC, best match is 42.22Vmp x 8 = 339.5V.

For minimum startup of 150V, the 51.27VOC x 4panels = 205Voc gives some clearance and should work okay, 5xpanels or more would be better to get Voltage up even in poorer light.

3xpanels with 3% Voltage tolerance would struggle to come on even in good light conditions.

@Taleb

I think your questions answered by @GreenFieldsregarding solar input. What is interesting is that i have not seen this model inverter in South Africa i could be mistaken. The Axpert VMIII 24v 3kw is quite a nice entry level inverter. Just take note that the 4kw 24v inverter is rated for 17A ac output that equates to 4000w ac, drawing 180amp@24v from the battery. It is therefore important to rate the battery accordingly. 100ah@1c would not be ideal as you would not be able to utilize the full potential of the inverter should you not have adequate pv available. Therefore i would suggest 2x 100ah 1c batteries in parallel to overcome the limitation. 

@GreenFields & @TaliaB

Thank you for your lovely responses.
I appreciate it.
Best regards.