============================================================================= 1. が is a subject marker. Here, the first が is attached to 人, and the second is attached to こと. Refer to this Tae Kim video for the usage of が
2. の is serving as a sort of noun here. This is a common occurrence in Japanese, where non masu-form and te-form verb phrases modify a noun. An example would be 水を飲んだ人 (in English: the person who drank the water) (lit: water drunk person)
Here, 普通の人ができない modifies こと. That こと has been できた and the entire verb phrase modifies の.
— の by the way, for all intents and purposes, is the same as こと except more subjective. Consequently…
============================================================================= 3. Adding の to the end of a verb is simply like adding こと to the end of a non masu-form or te-form verb.
At my level, I’m actually satisfied with understanding meanings. But in the real world, I think it doesn’t really count because they look for JLPT certificates and that’s the thing that’s annoying. Haha. Or maybe that’s just me.
Re: Minna no Nihongo
The one I have is 初級で読めるトピック25.
It hasn’t been 24 hours since I used it, but it contains a lot of articles for reading comprehension practice. It has exercise questions at the end. Also an answer key is provided at the back so you can self-evaluate. The main textbook I used for grammar is the Genki series, which was okay.
Yes, this makes sense. (Although I find that in many cases native Japanese speakers are able to figure out the implied subject (or in this case, the person/people who were able to do the thing) easily from subtle clues that I completely miss, so I can’t be sure that such a clue isn’t present in this sentence.)
Textbooks are full of out-of-context sentences, so it wouldn’t be unusual if it had been. (And Japanese sentences which often don’t use so much as a pronoun are not fully understandable out of context.)
However, みんなの日本語 does sound interesting based on the fact that I like ninjas.