Starting point should be Ahmedabad for the city is well connected to many parts of India. You could fly or rail to Ahmedabad. From Ahmedabad Bhuj is 6 hours away. From Bhuj Kutch is 5 hours away. From Kutch Gir national park is 9 hours away so it’s better you take a train. There are trains till Junagadh and then you have to take a cab to Gir park. From this national park Ahmedabad is 7 hours ride. So this is my suggestion Ahmedabad-Bhuj-Kutch-Gir national park and Ahmedabad.
First you should reach Ahmedabad from Mumbai. Ahmedabad is biggest City of Gujarat with number of Heritage Sites. in Ahmedabad you can visit Sabarmati Ashram Jami Masjid Bhadra Fort Teen Darwaja Hathee Singh Temple Swaminarayan Temple Kalupur From Ahmedabad catch night train Or bus to Bhuj Next Morning you will reach Bhuj. Explore Bhuj City Parag Mahal Aina Mahal Hamir Sagar Lake Kutch Museum
From Bhuj Go to Rann Utsav Dhordo village, Kalo Dungar, Great Rann of kutch along with Dholavira
Connectivity from Mumbai by flight
Ahemdabad and bhuj and Rajkot
by train also Ahemdabad,Bhuj and Rajkot are well connected from Mumbai.
Start your trip from Bhuj and end trip from Ahemdabad
or otherwise there is also flight from Ahemdabad to Bhuj if you start from Bhuj -Junagadh and -Ahemdabad.
Ahmedabad is center point , you can start from ABD, ahmedabad to bhuj distance is 6 hr, and ahmedabad to Gir distance also 7-8 hrs , so its upto you which place you want to cover first Bhuj or Gir.
Kutch, ahmd & gir are 3 different places and are distant to each other. Ahmdabad being center point for connectivity. I would recommend to take direct flight to Rajkot which is near to Gir then head to kutch and end at Ahmedabad. From ahmd you can go back via flight or even train. Between these cities you can travel via bus or book taxis whichever is convenient for you.
If Gir interests you, plan saurashtra tour. Ahmedabad, kutch all would be difficult then.
Reach Junagadh. plan to visit Girnar. Ropeway also available. Then visit Somnath, dwarka, Nageshwar jyotirling, Diu, porbunder can be covered