>> EW:
Given that a fleet can be spread over an arbitrarily large volume of space, I don't think a "Fleet" system would work. For the other two, modelling after SFBs EW system might work better. In SFB, ECM systems give a 1 point die roll shift based on the square root of the points difference between Ship A and Ship B.
Ship A has 1 ECM point, Ship B has no ECCM, 1 - 0 = 1 => 1 point shift on all fire by Ship B
Ship A has 5 ECM point, Ship B has 1 ECCM, 4 = 1 = 4 => 2 point shift on all fire by Ship B
All ships are limited to 6 self generated points, but can accept points from natural sources (asteroid fields, nebulas, other energetic space terrain, etc) and Scouts. Scouts are specialised ships, with Scout Channels replacing heavy weapons. Scout Channels cost power to activate, and once active can be used to "lend EW" (paid for with more power) to other ships within 15 hexes (1 hex = 10k km, conveniently enough), including enemy ships as "offensive EW", which counts towards the ECM values of any ship *targetted* by the affected vessel.
Obviously, the concept doesn't translate directly, because Aurora doesn't use die rolls, but you could convert the concept to fit :-
Make ECM systems a variable size system, which draw reactor power from the same power pool as weapons. Larger systems can draw more power in total (5 points per HS, or whatever), and the actual number of ECM points produced is multiplied by an efficiency rating derived from a separate tech line. Each tech level produces 10% more ECM per power point
A 1HS, efficiency 1 ECM component can produce up to 5 ( (5*1)*1) ECM points
A 2HS, efficiency 3 ECM component can produce up to 12 ( (5*2)*1.2) ECM points, etc
ECCM systems are similar, but smaller (maybe 0.1 HS size increments) because a ship may need many of them.
When fire is calculated, the EW calculation is (sqrt((targets total ECM)-(FCs total ECCM))*10% = fire adjustment value (deducted from beam hit %ages, or missile lock ranges, negative values treated as 0). Lending ranges are a function of component size and tech. Larger ships (which can support larger EW and power installations) and higher tech ships therefore get an advantage, but not a crushing one. Fleet EW ships, with extensive facilities, can radically affect combat outcomes. A fleet with extensive Scout support can beat a larger / better weapons tech opponent by rendering their weapons ineffective.
You would start needing to get into power management for ships though. If the reactors suffered damage, and available power reduced, how would it be distributed between weapons and EW systems?
SFB also has rules for crew quality and EW. For Aurora, crew grade could also be a consideration. A ship full of green consripts on their first cruise aren't as proficient with EW systems as a combat-hardened veteran crew. Spoilers can have advanced versions that produce more base points per power applied, salvageable and researchable in the same way as their other unique techs.
>> Ground Combat:
I definitely think a more detailed ground unit model would be nice, but I'm not sure about adding ground combat locations. I shouldn't need 10 PDCs to properly defend an asteroid. Since even quite large non-homeworld colonies are going to be pretty small places, I don't have a problem with modelling them as point targets, simply controlled by one side or another.
Now, a more detailed ground unit composition system, so you can build tank heavy / infantry heavy / etc formations would be interesting. The existing unit types do a fair job of approximating different unit roles, and as you can build BTN => BGD => DIV, you can customise a force quite a bit now. Increasing granularity to company level would let you custom build BTNs too
>> Supplies
Starship maint supplies are for starships really. The mineral costs are duranium, uridium and gallicite, so it's essentially structural spars, spare scanner and engine pieces. Do you really want to have to manage another category of "supplies", just to do something you can already do? Even a size 1 AMM is 2.5 tons, massively larger than any ordanance ground troops could realistically use. Even a heavy modern ATGM is only 20 - 25 kg, not including launcher / mounting gear