This is MY Theory on what life on Gallifrey was like before the Great Time War and why the Great Time War actually started.
My Theory - Life On Gallifrey Before The Great Time War
Life on Gallifrey would probably be just like life on Earth. The amount of people on Gallifrey is unbelievable. It's known that there were billions of Time Lords living on Gallifrey. 2.47 billion of them were children. I expect there was more than that though. Before the Great Time War all of these people would have lived normal everyday lives just like us.
Villages, towns and cities would all be in place where all the people of Gallifrey would live.
The people in the villages would've lived in a small community with a population of about 150-200 people per village. Each village would all consist on having a school for the children. Now the schools wouldn't be like an ordinary school. The schools would have the same type of lessons but all based around Gallifrey. For example we have English lessons, they would have lessons on how to speak and write in Gallifreyan. Maths lessons would be learning about co-ordinates and how to travel to places on Gallifrey via these co-ordinates that thy have worked out. Geography lessons would be learning about the landscape of Gallifrey. For example the mountains of Gallifrey. Maybe there is a Mount Gallifrey? They would also study the lakes of Gallifrey."Lake Gallifreyan" maybe? Obviously there would be a history lesson too. This would be a key lesson. This is where the children would learn about the creation of Gallifrey and where it came from. There would also be a Design and Technology lesson. Now this lesson the children would be able to learn how to build and put together a TARDIS. How cool is that. You get the idea.
Towns would be pretty much the same as the villages but with a more higher population per town. Probably about 500-550 people. With more shops for the people of Gallifrey too. Schools would be in these towns too.
Cities would be quite big obviously. The cities would be made up of both housing estates and shopping centers. The population of the cities would be about 3000-4000 people. 5000 maximum. Schools would also be in the cities. In fact quite a few schools per city.
All of these places would be scattered around the whole planet. With Gallifrey Citadel centered right in the center of the Planet.
The only mode of Transport around Gallifrey would only be TARDIS. Using the co-ordinates they learned in their maths lessons, they would apply this knowledge to enter the co-ordinates in the TARDIS to get them to their desired location. See school lessons do come in handy.
The city would also be full of countryside too where fields and parks would be based.
My Theory - How The Great Time War Began
The High Council of Gallifrey are having a meeting. They are looking at the future of Gallifrey and see how it would look like in the future. During their meeting they would have look via their screens in the room. Entering a specific code on the database that has restricted access for others. Things all start to look all bright and beautiful until they notice one thing. They notice that the evil creator, Davros plans on creating a load of Daleks to take over Gallifrey. Davros has been monitoring Gallifrey for years and has grown jealous of their equipment and technology. This is why Davros wants to create the Daleks. They summon the technology team of the High Council to hack into the database to collect co-ordinates to this place. They hack into the system and find out that Davros is on planet Skaro. The High Council need one brave person to travel to Skaro and kidnap Davros and bring him to Gallifrey so they can contain him and keep him under control. One man steps forward, the Doctor!
The Doctor is given the co-ordinates and enters them into a TARDIS to travel to Skaro. The Doctor lands Skaro and tracks down Davros. He tricks Davros into coming to Gallifrey by saying the High Council were going to grant him the technology for his Planet. Davros being Davros fools for this and joins the Doctor in the TARDIS.
Back on Gallifrey, the Doctor hands Davros over to the High Council. They take him to a room where they isolate Davros. Davros is contaminated for years and years. Life on Gallifrey continues as normal. But what the Doctor doesn't know is that Davros has a test model of a Dalek that has the same brains as Davros. The machines on Skaro are ready to go with millions of Daleks ready for processing. The prototype Dalek takes control of the control room and begins the process.
Once these Daleks have been fully assembled they notice that Davros' absence has been going on for many years. Davros' controls on him have a tracking device in which Davros can be tracked. Once Davros has been located the prototype Dalek takes control and sets a mission for his fellow Daleks. Destroy Gallifrey and retrieve Davros!
As time progresses on, the High Council of Gallifrey notice that one by one a village is being wiped out and destroyed from Gallifrey killing many people. They have no idea yet on what is doing this and whether or not they are being attacked. Things get more serious when towns and major cities are starting to be wiped out. The High Council scan the entire planet to trace any other life form in their world. They pick up traces of a species called the Daleks.
Over the years Gallifrey would slowly be destroyed meaning one thing for the Doctor to do. Destroy Gallifrey for good. This is using "The Moment" as seen used by the War Doctor. But as seen in "The Day of the Doctor", Gallifrey is frozen by the The Doctor(s) and have hidden Gallifrey away in a "Pocket Universe". Meaning Gallifrey is out there somewhere! We just require the co-ordinates to get there.
There You Go
So after all of this the war and battle would go into the Time War book. This is my theory on the Origin of Gallifrey and how the Time War began.