Depth Sounder and Speed Sensor

[NeverlandSail]

Hi all, I hope this is the proper thread to pose this question.
I recently bought my first boat, a 1981 Catalina 30. I’m rewiring my old NMEA 0183 System to a newer NMEA 2000 setup for my knowledge and experience. As I was doing my research and prep, I discovered that my boat does not have thru hull fittings for either my depth transducer or speed sensor.
I do not have a paddlewheel, my speed is only SOG from a small GPS unit mounted on my Bimini. My depth transducer is in hull, just forward of my keel. I would not like to drill holes for new fittings.
Are there are NMEA 2000 compatible depth transducers in hull fittings you all recommend?

Secondly, I am planning to buy new instruments (since mine are badly sun damaged) and was looking at the GNX 20’s. Can this model display information like my TWA, position, and SOG from a small GPS satellite?

For my depth transducer, could I buy a GDT 43, then sink it in antifreeze/mineral oil in the old in-hull fitting?

Lastly, are there any NMEA 2000 small gps satellites you
recommend buying, that provide SOG etc.

Thank you for any and all answers, I appreciate it. I hope my train of thought is on to something!