you don't pick specific targets for your navy and whatnot, but regions and orders. Adds so much more you can do without increasing the CPU load.
battles start small and slowly trickle in with reinforcements with starting ships and reinforcement trickle based upon your fleet's concentration. Having good Sensor coverage of the area (provided by planets, fighters/bombers, scout ships, and a small amount by normal ships based upon concentration) determines reinforcement rate and how easy it is for your fleet to find the enemy and high levels can make retreat extremely difficult.
Should add supply, but abstract it out with simply building convoy ships added to a pool, these can be destroyed to strangle a large fleet, applying attrition.
Sneaky ships can sneak up on enemy fleets reducing the effect enemy sensor coverage has on them allowing them to quickly hit convoys and then run.
Fleets have a optimal supply range, but can be told ignore the range to start taking supply attrition, with possibly different modes on how far they'll go in supply before returning home to resupply(merely turning off the effect). battles outside of their supply range will have to wait longer for reinforcements to start trickling in.
build forts to extend your supply range around them, less than stations, and frontier outposts add supply range comparable to stations.
This gives you multiple avenues to attack enemy fleets. Give orders for a few different things.
Siege - go after planets, start hitting the planets in the region
interdiction - try to start many battles to slow the enemy down, reinforce the smallest battles and retreat from ones where you get outnumbered.
Search and Destroy - Try to find enemy and start a battle, then pile onto that battle. Can still make multiple battle but less so than interdiction
Convoy Raid - focus on convoys and retreat from other battles that don't involve them.
Protect Convoys - try to assist convoys and retreat from other battles.
Scout - retreat from battles but provide sensor coverage.
FYI, retreating would be like HoI4, where ships have to pull out of battles, the distance being determined by sensor coverage.
Also look up HoI4s current naval combat to see how combat would be processed, using ranged, fight/bomber, submarine tactics etc.
etc, etc, etc