Hi
At first the Displays looks good. ... Important here is: It must be common Cathode .... AND It should have a good PIN System ( 13 in that case is perfect)
About Max Chips.
If you plan to build a own PCB you can simply buy Max Chips and you can solder it (including the whole wirework in lines on the PCB )
If you plan to simply connect those MaxChips via 5 wires to the Mega and via wires to the Displays then i recommend "MaxTubes" ( with removeable Diggits)
Something like this ....
https://www.amazon.de/8-Digit-Display-MAX7219-Digital-Control/dp/B00P9277BE
Buy those kind (green pcb) that alow to remove the 2x4 Blocks .... Then you can simply connect your 1x5 Block on it with wires and some solder work.
About number of Max Chips.
In Mobiflight a Config is located alwaysto ONE Max7219 Chip..... If you use a 5 diggit Block for example on digit 1,2,3,4,5 then all is fine and you have no Problems.
If you like to use the 3 empty Diggits now with another 5 digit Blcok you got a problem.
Example:
Display A (5 diggits) is set to MAX1 pin 1,2,3,4,5 all is fine !
Display B (5 diggits) is set to MAX1 Pin 6,7,8 AND Max 2 Pin 1,2, THEN thsi is difficult maby
Display C (5 diggits) is set to MAX 2 Pin 3,4,5,6,7 all is fine again.
You see.... Its much more easy and recommend to set a Display only to ONE Max Chip and not "crossover" between two chips.
*****
Summary.
I personaly recommend to use ONE Max for ONE Display logic.( much more tidy, logical and clean )
If you realy care about the now empty 3 pins on each MaxChip i recommend to use 3 Diggit Outputs ( like CRS, HDG and so on) for this.
(Whatever a Max is realy cheap.... i would not care about that unused pins)
Finaly i NOT recommend to split Displays over 2 Max Chips. Its possible BUT you need 2 Configs and you need some advanced logicsto split them !
In Easy words.... If you need 8 Blocks with 5 diggits i would simply buy also 8 Max Chips!