If you want a -X% sensor range per component system, you may as well impose a flat limit on the number of sensor components you can add to the ship and forget about the stacking penalty.
Pretty much, yes.
There's a maximum sensor range which the game's mechanics can handle properly. Once you figure that out, ensure that the biggest hull with all the bonus space techs loaded down with sensors has THAT sensor range, and then make everything else a percentage of that. Problem is, a huge hull with all max-tech sensors on it has a vast range; so vast that you can't make it into a sensibly-sized portion of the map without making early-sensor small ships essentially blind without basically saying at some point that sensors don't have any further positive effect.
A flat cap of X would work for that, so would a diminishing return (not necessarily just -10% ship-wide sensor range per sensor, as the previous system allowed for - it could be that each NEW sensor is 10% weaker than the last, so 1 sensor has 100%, sensor output, 2 sensors 190%, 3 sensors 271%, 4 sensors 344% etc).
Ok, so I only play on Insane maps. I play with RARE habitable planets and I play with A LOT of races. As a poster above state just play on smaller maps. Uh, no. Play 50 races, abundant minors abundant stars and planets but make your hab ones RARE and you will find a much different game. Having things like sensors, engines and life support scale to map size will give you the same pacing on a small/medium as here on Insane. There has been a lot of discussion on having some things tied to map scaling. I am all for it.
To be honest, if you scale exactly (i.e., map 10 times as big, movement multiplied by 10) then it's not the same pacing. It's just the same game. The only difference is lots of empty space and dead planets, which may as well not exist because you've increased the move speed to travel across it just as quickly and the sensor radius to see just as far. You really may as well just play on the smaller map, otherwise a bigger map is basically just a way of benchmarking your PC rather than a different gameplay experience. The game will populate the races and minors in addition to the rare planets regardless, so really you're not changing much between, say, large and insane - you just get like 2 more minors and a more or less equal % of additional planets.
Map size really ought to have nothing scaled off it at all. I could see an argument in favour of scaling speed on the Game Pacing setting (so on fast everything is 3 times faster than on normal). Not from the map itself. though, and certainly not with massive and draconian reductions in engine speed and sensor strength (otherwise we'd be straight back to the start with all the problems caused by having very very fast ships or very very long-range sensors).
Research should be as Naselus mentions which should be tied to number of hab planets on map creation. Only got 200 planets on the entire map? Well you are going to take a loooooong time to get stuff done, especially if you have 30 majors and 25 minors.
Not to hab planets - to #of habs divided by # of races. 200 planets with just 2 races will tech a lot quicker than the exact same map with 50 races.