Welcome to the forums! Congratulations on going to one car! That is great.
Decisions like these are personal, and you will likely get different advice from reasonable folks. I hear you saying that safety is important to you, as is making the most financially responsible decision. Plus the car has to look nice enough to drive a client around once in a while.
"Safe" is a fuzzy term. The safest thing you are doing is not driving much. :) In terms of straight-up crash testing, your 2013 Civic is probably "safer" than the 20 year old Integra. Manufacturers have made numerous changes to car body integrity and seat angles in the past few years in response to the IIHS's new offset, side-impact, and rear-impact tests. But if you are driving infrequently, and mostly in the city, these differences probably don't matter much. The kids will factor into your safety determination once they arrive though.
Financially you are probably better off selling the Civic and sticking with the Acura for a while. Since you are driving very low miles, the Civic's gas mileage advantage doesn't help you much. So you are better off getting rid of that loan, even though it is very low interest.
If it was me, and if the Acura looks good enough for clients, I would probably sell the Civic, invest the proceeds, and stick with the Acura until you have kids. At that point your Acura will be ~22 years old. I'd thank it fondly for its years of loyal service and then sell it. I'd look for something newer and bigger (bigger = safer, plus you don't want to be clicking car seats in and out of the Integra, I speak from experience). Something like a 5-10 y.o. Camry or Accord hits the "family sweet spot" for a lot of people. Reliable, big enough back seat, good safety ratings, still gets decent/good gas mileage. And would still be "nice" enough to drive a client around.
Good luck!
