Book government ferry in advance to save money. Private ferries will be costlier. Look for airbnb as you are traveling with family to save cost. For travel go and negotiate if you are taking four wheeler. If you are interested in water activities you can do scuba diving in Havelock island starting from 2000.
I tried booking on Ministry website but no ferry service available. Could you please mention website. I'm planning for Feb month.
@Pratikkkkkk can help he is from North Sentinel Island
Arey bhai @iron-man , if you’re really planning to travel to Andaman, don’t miss visiting our North Sentinel Island. You won’t find such friendly and welcoming people anywhere else in the world—it's truly a one-of-a-kind experience!❤️ 
Book govt guest house and ferry
Anadaman teal house portblair
Dolphin resort at havelock
Hawa bill nest at Neil island
Reasonable price decent room
Book flight in advance to portblair
Day 1 and day 2
Portblair sightseeing like jail ,museum and few beaches
Ross island & northbay island
Day 3 and 4
Havelock island
Scuba diving
Activites at elephant beach like snorkeling
Radhhanagar beach for sunset view
Kalapathar beach
U can go for kayakaing at midnight for bioluminescent (crazy experience)
Day 5
Neil island
Beware of crocodile attacks on andaman beached
I'm Also Planning For Andaman on First Week Of March
Great writeup, very informative
Book govt guest house and ferry
Anadaman teal house portblair
Dolphin resort at havelock
Hawa bill nest at Neil island
Reasonable price decent room