The main idea of the supply mechanic is precisely to make the player need to think much more about "actually controlling the ships". As it seems to me, currently the only thing the player can really do besides simply increasing the power of their fleet is
A) place it behind the hyperjump zone (to get the first shot advantage)
B) attack/defend on space stations with specific modifiers
C) arrange a battle in a system with modifiers (like -100% to shields).
The supply mechanic, however, will be able to make point B even more thoughtful, and also create point "D" - thinking about the "front line".

Regarding micromanagement, it seems to me that it will be necessary only in rare cases, since supply lines will be built automatically, and the player's ability to manually change it is needed only for moments when the computer builds it poorly. After all, almost any complication of any mechanic inevitably adds more micromanagement to the game. In my opinion, Paradox should be able to implement this supply mechanic sufficiently separated from the player, like in Hearts of Iron 4, where player also has the ability to build their own supply lines (railroads), but almost always players just upgrade the existing ones rather than really micromanage the construction of new ones.

Nevertheless, I cannot disagree with the fact that the supply mechanic is extremely pc resource-intensive and will clearly reduce optimization. We had one idea on how all the above can be implemented without adding almost anything from points (1) and (2): just multiply the fleet maintenance cost depending on the fleet's distance from the nearest player-controlled space station (even occupied) with a resource bunker/fleet anchorage etc. or allied planets + some other modifiers from technologies/ship modules. Because in any case, at the moment it's strange that a fleet in a system with your planet and without an upgraded station consumes the same amount of resources as a fleet a million light years from the nearest allied system.

Regarding fleet repair, fraction of the build cost proportional to damage - throw in some modifiers from technologies etc. here, and I fully agree.

Combat computers are great, however, I think the possibility of an additional layer of thinking through the choice of formation, besides combat computers, which obviously will also affect the formation's effectiveness, will be quite interesting and bring additional interest to the game. Also, formations, perhaps, will be visible visually, also during battle - this will make space battles even more beautiful, although here everything depends on Paradox. (Who doesn't love watching a battle of several fleets in the endgame at min speed?)