. 1) Is this correct configuration of basin/pan?
Sounds correct to me.

. 2) It appears a per-longed defrost would be needed to correct some of the issues, is this correct?
I do not think so.
Sounds more like the drain tube is plugged so the water from defrost is accumulating and finally overflowing.

I would check that it is clear.
If plugged a turkey baster with warm water, an air compressor with low pressure or a wire can often be used to clear it.

Also check that it is not plugged with dust etc. at the drain pan end.
You might as well clean the condenser/compressor fan and the condenser coils while you are down there.

If it looks like stuff is growing in the tube I would flush it with a 10% bleach solution. This should kill the stuff and let you flush it out. You may have to do this several times, let it sit for 15 minutes or so between flushes.

Be careful that the drip tray does not overflow and empty the drip tray after you are done.

Be sure to unplug the unit while doing this.

Also check that the pan is clean any dirt/film on it will slow down the eater and cause problems. Sometimes a coat of buffed up wax helps.

If all OK then there is a jiggery pokery for drain defrost but the above should fix the problem.