The ignition systems for all 90s hondas a pretty similar and make them easy to steal. A popular trick is the use of shimmy keys, these are heavily used car keys that are flattened out and modified slightly to unlock and turn on pretty much any <2000s honda. An aftermarket alarm is almost a must for these cars depending on where you live. Just having that blinking light around the dashboard somewhere is enough to deter would be car thieves.

These be as easy to steal as old motorcycles. Legit screwdriver and a wire coat hanger is all you need if even that. If you like the del sol then just get some anti-theft devices on the car. Wheel locks, kill switch and all that.

I would imagine theft rate is about the same. As others have said, even a beginner car thief could steal one.

A kill switch is the best option to deter theft. I've actually seen cars driving down the road with their alarm going off, so not really sold on alarms as a preventative measure. Plus these days people will just pull out their cell phone and use the theft as Tik Tok content while screaming "Oh SNAP! Oh SNAAAAPPPP!" rather than do anything to help. An alarm pretty much depends on those around the car to take notice and do something. In today's society? Not happening.

Yes

If you plan to buy one, make sure you install a kill switch or remove the fuel pump relay wherever you park. 

I would put a removable steering wheel on as well.  If a thief wants a car they will get it. Just make it harder for them to steal.