Take a look at Starmada Admiralty edition rules annex. It has a rather simple system you could use for a multi sector wide war. It boils down to 5 different elements for the game which you can use.
Fleets self explanatory it represents a fleet of starships
GDF ground defence forces. Anything used to defend a planet that cannot travel FTL by itsel.
Small, medium, large instilations. Small instillation will have the bare minimum to keep a fleet going. Refueling, some minor repair. Medium instilation this is what most people are used too can refuel and repair a fleet and keep it going. Large, this can do everything a medium can do but also where new fleets will be built and deployed. Large instilations are the Depot system or a large naval base.
In the game these are known as outposts, space stations, and starbases. However in the Traveller game these represent different facility sizes.
Here it boils down to collect income, pay maintanace, psy for improvements, buy new forces. Then decide how to fight.
All counters save for Small instilations have a crippled and normal side. You can either pay to have the unit fixed or in the case of fleets and GDFs you can merge two to make a normal one.
Supply is important. No supply cripples you automatically. Outposts or light instilations are destrioyed automatically in a no supply status.