Should you decide to spend a part of your rank 5 salary on fast tracking fortifications you take the most comfortable rout to maintain rank 5. It is nothing wrong with this, but please try to fortificate only systems that have not met the trigger for succesful fortification yet - else your efforts would be wasted for your power - and this would be a shame, wouldn't it?
You also can decide to ship your fortifications only to the nearest controlsystem, regardless if the trigger is met or not and grind the fastest possibel way to earn your cash. But dont be offended if you will be called a useless grinder then.
You also can scout the powerplay map for the most profitabel systems your power could expand to - mind though that you have to substract the overhead count from the shown CC profit on the map and also on the side-tab. This means that actually many systems that show positive CC-values actually are lossmaking systems. If you chose to prepare a system you can apply the same fast-track system as with fortifications.
If you like fighting, you can try to undermine - but best try it only in anarchy systems until you are shure you know what you do - or shoot your way through expansions or oppose enemy expansions. But mind that for many powers (mostly the combat oriented ones) expansions are bugged and as much fun as shooting sitting ducks.
And if you would like to commit yourself to a powerplay community - dont hesitate and look into the according reddit page of your faction and see if there are still some active members there.
Take care and always remember: great power also brings with it great responsibility!