please let me know what capacity of generators will I use to comfortably supply power with these paramitter readings.

420 A 240V = ?

123 A 240V = ?

You should give more details of load like-lights & type, heaters,furnace,motors & type/starting methods/sequence, diversity factor,load factor etc,power factor,induction furnace etc,and refer manufacturers catalog on "generator sizing" by Caterpillar or any other reputed manufacturer.