These are pretty good observations for someone who has never had a lesson! I train so that I can take these at full bore! There are Aikidoka out there that could probably hurt you if they wanted to, no matter how good your ukemi was (ability to fall), but that's not the point. There are also Aikidoka out there that you couldn't hurt if you tried, because their ukemi is so well developed.
Have fun on your new adventure! Best of luck and Don't get hurt!
I'm sure you are correct. If your ukemi is good you can probably limit the damage but I would imagine the average thug on the street wouldn't be able to do much against a properly applied technique.