This is mostly a re-alignment of forces and civilian personnel who are already doing the job (of which there are many, across multiple services). There is actually little additional cost here...I think $2B over 5 years...which is a small portion of the $738B defense budget.
Mostly with debt. Initially it's only $40m, although will probably get more expensive over time. Previous secretary of AF predicted $12 billion, but I think that was with a version of the plan that was more involved (such as USSF taking over the NRO)
Debt, the same way the US pays for literally everything
Taxes and debt.
Until a corresponding increase in taxation is made to pay for a new expenditure. The new expenditure is paid for entirely by debt.