Re: Aikido on the ground, questions.
Yes, if you are interested in the self defence aspect of martial arts you need to address the quetion of ground fighting. It may be possible to make some use of Aikido fundamentals on the ground, but only in the sames sense that it may be possible to use some things from an aerobics class in a boxing match.
In other words there are better quicker ways to gain competency - while continuing to use Aiki principals.
six months or so of good BJJ training will be enough for you to tick this box against the average assailant (i.e. give you some skills to control position and regain your feet).
Or you could do Aikido for 10 years for a much less return in terms of ground fighting (although countless other benefits).
So if you are concerned about self defence, do BJJ (or newaza focused Judo at a pinch, or wrestling) for a while alongside your aikido. Just be prepared for the fact that it is addictive and you may not want to stop after 12 months.