Building a space navy

Strategic Assumptions
Why does your navy exists? Everything has a purpose. Space Navy is not different. Czech author of military sci-fi Jan Kotouč explains.
The Six Steps of building a navy:
Strategic Assumptions
Strategic Goals
Fleet Mission
Fleet Design
Force Size
Force Management
Strategic Assumptions
Why do the Starfleet from Star Trek, Imperial Galactic Navy from Star Wars, Battlestar Galactica, Royal Manticore Navy from Honor Harrington series exists? What are the basic realities, called Strategic Assumptions, that we need to take into account before we start building our navy.
Security Environment
What are the potential threads?
Why do we need our navy?
Who are our enemies and friends?
Do we need to defend or attack?
Fiscal Environment
Navy is expensive.
What can we afford?
How large is our economy?
If we have resources, do we have the know how how to develop them into a space ship?
Building a space navy requires a multiple industries and specializations.