Well what I think is somewhat irrelevant, you should do what your dermatologist says. Although of course there is no harm in floating the idea of a short extension past him But to have a few small spots at the end of your treatment is normal, your skin will look best in the months following the completion of your course. I would try not to fret too much about things which are largely out of your control, you took the step to go on accutane, trust it to work for you.
Well if your acne has cleared up completely and your dermatologist is satisfied with your outcome I can't see why you should have to do any more. It seems like a pretty standard course that you've been put on which generally has a high and sustained success rate. Certainly very similar to my own at least Accumulative dosing only works up to a point, after that you're just taking medication for the sake of it.
From my own experience my skin has just gotten better and better since I came off accutane. I've been off 18 months now and my skin is now the best it's ever been. All I do is wash my face at night with a gentle facewash, and apply a bit of moisturiser each morning (nothing like the amount/frequency you do when on accutane). Your skin will be slightly drier than average from now on, but it's such a tiny price to pay for not getting acne anymore. Simple things that were initially horrendous are now easy, like being able to shave without ripping your face apart. Well anyway, just to reiterate - enjoy your new skin, it's uphill from here. The red marks will take care of themselves
Yeah red marks during accutane suck, most people see a noticeable lack of healing during their course as this is just the nature of how the drug works. My advice? By far the best product in the healing of red marks is your own patience. You can waste shedloads of money and hope on creams designed to increase skin turnover or reduce the appearance of red marks, but the reality is these will make at best only very small improvements.
You're much better off relishing in your no longer acne-prone skin and just letting time do a good job of clearing up your red marks. They will go away, just be prepared to be patient. In my own experience it took 7-8 months for the very worst of them to go. A long time yes, but the knowledge that they're not going to be replaced by new ones thanks to accutane was great, and after about 2 months I stopped caring about them completely.