You can build a unit as a single 200,000 formation. Good luck in moving it, you will need 200,000 tons of troop transport bays on one ship, thats probably going to end up as a 4-500,000 ton merchant ship which will be hard to build
Most people typically build formations of 10-25,000 tons and then assemble them as larger formations under larger HQ's. For instance my Legion is 220,000 tons total(approx some units are slightly smaller than notional)
consisting of 20,000 ton Legion HQ with a 220,000 ton hq. 10 Cohorts each ofa notional 20,000 tons with a 20,000 ton HQ . I then have a consular HQ of 1000,000 tons capacity commanding 4 Legions and support assets, that HQ is also 20,000 tons as a unit.
My troop transports are 100,000 tons like most of my commercial shipping and each lifts 40,000 tons of troops, typically grouped in formations of 6 ships lifting a legion and a supply cohort.

That would be about right

Would having 7500 ton ships mixed in with the 750 ones affect the sensors adversely

I have resolution 120 which is 6k tons?

I see now a few of their new ships are 750 tons

yep range perimeter is up

after salvaging a wreck thye have sensor jammers and cloaking - is this going to be it?

I’m having a border dispute with some baddies and in the past have been able to target the ships as they enter the sensor range - about 18m km

This last batch of baddies under the same classification managed to close to 250k km before my sensors would let me target them and then I fell within their energy weapon range

Is this new ability to close the distance untargetted likely to be a fancy new system they have - stealth or jammers - and is there a way to counter this