its breaking up into a lot of little topics
first, you only need one res5 active in your fleet, no matter how many ships are being supported. many res 5 MFC, but anyway those are a lot smaller and cheaper.
you can definitely accomplish your scouting/ spotting needs with fighters. i myself loathe the amount of clicking involved but some people actively enjoy it. i would still maintain a variant of ajax with a res 5 because fighters really do occasionally just disappear.
i don't feel like beam fighters are your principal concern. since you seem to have found a weakness there is no reason to not address it, but missile fighters are in my view more dangerous by far.
size 4 missiles can probably afford to mount a small active sensor. the overkill/ underkill dilemma plays out in more scenarios than just shooting at fighters, and if you're going for high range having multiple mfc in multiple resolutions is an extravagance.
155 spaces of goodies vs 220 spaces of carcass doesn't mean all that much; underpowered engines use a lot of space but not a lot of resources. i would say that ratio is maybe a little on the fatty side considering your engine power is as high as it is, but not unreasonably so and you made a conscious decision regarding range and endurance.
you definitely dont want a size 10 active on each of your ships, but having res 1,5,40,and 100 in your fleet is worth some expense. if it were me, i'd pick a class i intended to have ~8 of per fleet, just find the space for a size 8-12 active, and have 3-5 variant classes (the res 40 is good but optional, a thermal is good but optional). when your sensors are so big that this just doesnt work (ie the variants require a retool) it's time to bust out specialist sensor classes with their own shipyard. or, you know, clickety clickety click with dozens of individual AWAC type fighters everywhere you go
at 19000 tons, if your opponent has actives tuned to your size, yeah he's going to see you first and there is nothing you can do about it. in a first contact scenario (...which is where all of my battles happen) he's probably using res 100 or smaller, and so a fighter strike providing its own spotting has a pretty good chance of being detectable. (size 10 res 5) > (size 2 res 100).