Thanks for the suggestions
The Essex class is meant to be the 'first wave' early jump point defense after, and with, mines. That is why they have engines so that they can self deploy without needing boat bay or tractor beam RP. After getting either or both techs, dropping engine is a great improvement though! A similar idea is behind the sensors, the first few Essex will be all alone out there until the supporting designs get built. After the dedicated sensor platforms are in place dropping the sensors off the next version of the Essex makes sense.
I've also been looking at improving the mines, going to a size 6 buoy with a pair of Sprint II's and a bigger on board passive sensor. The size 6 mine would use the same launcher as a size 6 early warning sensor buoy to be deployed on the other side of the jump point. I'm a bit worried that the thermal sensor on the Blackjack II might be too weak.
As far as carrier vs tug, early on a jump capable 'jeep' (ultralight) carrier is much cheaper on RP (1000 for boat bay) and can be built on the early shipyards without much (if any) expansion. This greatly improves the mobility of the defense at a pretty modest cost. The problem then becomes more one of logistics, needing either (or both) forward outpost colonies and jump capable colliers.
Using tractor beam tugs seems to me to be more a later game idea, especially when your shipyard capacity grows enough that the use of the fighter production lines isn't as beneficial. At least it seems to me that tugs would go hand in hand with 'real' bases instead of the Essex style mini base.
Now if I could figure out how to make a viable beam weapon based Essex replacement without spending way too much RP, forward deployment logistics would get a *lot* simpler