It's a great starter boat. "For couples" just means, make sure the accommodations (galley, head, sleeping areas) are clean and in good working order.
Things to look out for are rust streaks dripping down from the chainplates for the upper shrouds or backing plates for the lower shrouds. That could be a sign of crevice corrosion. Another replacement I had to do was the brackets that hold the spreaders to the mast. If they are small grey triangles, they are cast aluminum and need to be replaced with a much beefier stainless. If the PO hasn't upgraded these systems, you will have to; fortunately both upgrades are doable for somebody with no experience whatsoever.
The engine is also a big deal. On lakes and you should be fine with a 10hp outboard; haven't navigated any rivers. However if you think you can do with an outboard, I highly recommend it; the extra space under the cockpit and quarterberths is cavernous.
What's the interior layout? I have a dinette layout and find it sort of cramped. The "traditional" layout, with a settee on either side, probably would have been preferable.
It's pretty easy to get replacement parts; Catalina Direct:
has lots of C27-specific stuff.
All in all I've been very happy with this boat. Just raced it singlehanded over fifty miles. Came in last, but another C27 tied for first in our class
Before that I have done a good amount of cruising in various conditions and always came through safely, though not always as comfortably as a real cruising boat would.