For Andaman keep at least 7-8days in hand as Andaman will take you by breath .. but both Goa and Andaman are contrast to each other. while both has beautiful beaches, goa is more of people, Andaman is only about nature..
Andaman is more family friendly destination and is beautiful. For one week trip to Andaman, with descent stay, scuba diving, sightseeing it will cost around 15000 per person excluding flights. So it will be around 25000 per person for one week trip. You can take up packages from Tripoto or you can plan on your own. If you want any help with planning or places connect with me. You can either message me in tripoto or in instagram @lifeoutsidecubicle