Father Tim is presuming that the first ship(s) to enter a system are survey ships. I don't. I have dedicated scouts for that. Before I have jump tenders, I build jump pinnaces in fighter factories. Long endurance fighters with single ship jump engines. Because one of my big concerns is revealing the jump point I entered, if that jump point emerges in the inner system somewhere. Small jump scouts are much less likely to be detected on transit.
Because I scout before the survey ships go in, the only surprises I am likely to encounter is if there is an asteroid base, comet base or listening post, and that is something my geo survey is going to blunder into at some point. And I would rather have it be small and cheap geo survey ship getting munched than an expensive all-in-one survey vessel getting munched.
I like the RP that you can't start researching jump engines until you find a jump point. Seems a little odd though, because you need jump theory to get grav sensors. But having a core RP that shapes your fleet policy, research makes for more interesting story, in my opinion.
As far as geo/grav survey fighters? I tried them. Unfortunately they just are not very efficient. Consider trying to get even 3 HS of engines in. That is 5 HS for sensor, 3 for engines, 1 HS for fuel... not much for engineering or crew endurance. You might be stuck with only 2 HS for engines, and that is really slow. I like 800-1000 ton for grav survey boats. You can easily put 6 HS worth of engines, 2 HS for fuel, decent endurance, and even a sensor. Or go up to 1000 tons and give them a single ship jump engine. Also, they are easy to upgrade that way with new engines.
Interestingly, you can conduct a survey with embarked survey ships. You get survey points for every survey sensor in the task group, whether they are flying independently, or inside a hangar.
Part of the problem with geo/grav survey fighters is that normally what you use a carrier for is long distance transport. You are either carrying something with no engines (like a commercial early warning satellite to place near jump points) or boosted engines. And survey ships have to do a LOT of travelling independently. You don't want boosted engines on a survey ship, unless you have a lot of tankers resupplying your survey fleet, and even then. Once you are supporting a survey group several jumps out, the carrier is at least useful for the jump tender capabilities and the ability to repair survey sensors. Small survey craft are unlikely to carry enough supplies to repair a maintenance failure in a survey sensor.
Operationally, there are a few other problems as well. If you have picked an engine boost level that gives your survey fighters any speed, you may choose to skimp on engineering and crew endurance. But this means you HAVE to recall your survey group to go anywhere, and they need to roll back their maintenance clocks on board the carrier a lot. Which can be inconvenient if the various survey craft return to the carrier at widely separated times because. And the micro is time-consuming, and the chances that you will forget, and move your carrier resulting in your poor survey craft running out of fuel is high. I could do without the message spam of xyz survey ship is out of fuel, thanks.
Optimizing TOO much on BP considerations can mean that managing your survey forces take a lot more time and attention. I like having a large enough endurance and fuel cushion that I only rarely have to worry about them.
I go back and forth on whether or not to go for commercial for geosurvey. The solution I ended up with was that my geosurvey ships double as tankers and jump tenders as well, at least the 2nd generation geosurvey. So I often have more geosurvey ships than I need, but they don't cost maintenance, and can serve some double duties. But you could go the survey boat (less than 1000 ton) strategy for geo survey as well, with survey support carriers and jump tender/tankers in support. Survey support doesn't have enough hangars to hold the entire group, just to hold any one craft that needs repairs, while generally transporting the boosted engine scouts and engineless jump point monitors that provide security as you explore.