I wouldn't recommend native speakers reading Huxley :-D But yeah, I don't see why you can't read him. Maybe your level is 'only' B-1, but the fact is that we get better through being exposed to new vocabulary and encountering new ways in which the language works, not by doing the same textbook exercises that we are comfortable with. Just take it steady, try not to look up too many words right away, try to figure them out by context; underline them if you really can't work it out, see if they turn up elsewhere. Good luck.

You are correct, the latter two sentences cannot be used. Made, in the sense that it is used above, implies some kind of coercion, in that somebody was forced to do something through an action of your own. Had, in the sense you use it first, is a strange one, and although correct it strikes me as an Americanism (but since you are Korean I am assuming American English is what you are used to). In that sense all it means is you arranged that a certain person would fix your car; there was no coercion, you and the mechanic agreed a date, and a time, and a fee; you had him fix you car. Made works for sad because somebody's actions resulted in the sadness of someone else.

Which we use for non-restrictive clause; that we use for restrictive clauses. A non-restrictive clause is used to add non-essential information. Let us say you wish to tell us of your unreliable car. My car, which is ten years old, broke down last Saturday for the eighteenth time. You use 'which' to add ten years old; the information is non-essential as it is not central to the facts of the story. In a sentence using that: I was driving to the store in my car that breaks down all the time. Your central point is that your car breaks down all the time. Notice that which is accompanied by a pair of commas, no such thing occurs when you use that. So: 1) You will hear us talk about the Russian joke again, which I’m fed up with frankly. Yes: You will hear us talk about the Russian joke, which I'm fed up with, again. (That you are fed up of the joke is not the key information, so you can use which: a non-restrictive clause) 2) That’s a very simple game which people play with their friends just for fun. It is a very simple game that people play just for fun. (That it is just for fun and not competitive is vital information, so you need that) 3) I’m now going to read out all the “would you rather” questions which that you’re going to hear in this episode. I'm going to read out all the 'would you rather' question that you're going to hear in this episode (again, that they are going to be heard during this episode is vital so you need to use a restrictive clause). 4) Would you rather… – 
Have accordions for legs? – 
Or have a huge belly button which is 10 inches long and that sways to the beat of popular music? 5) Would you rather – be very very fat (clinically obese)? – or have Tourette’s syndrome? (that’s a mental disorder which means that you randomly shout out very rude words in public and you can’t control it). For both of those you need 'that' as they identify key element in defining the belly, and Tourette's syndrome.

Haha, what are you reading? You are getting into some technical stuff here. Okay: So, the text is about a Holocaust memorial site, right? (Is it the Berlin Holocaust memorial? It sounds like it... my reason for asking will be clear) But the site (if it is the one I am thinking of) is not a representation of the Holocaust, correct? There is no attempt to recreate a concentration camp, or to make a story out of some props. So, on a purely visual level it is not 'obviously' any one thing. And yet, as visitors we know it is a Holocaust memorial, and because it is a memorial, we know what kind of behaviour is expected from us when we visit. The term (written, spoken, whatever) 'memorial' is a "sign" that we understand to signify certain expectations. In short the 'sign' refers to the concept of memorial; 'party' would be another sign, 'funeral' another. Does this make sense for you? That's the simplest I can put it; I hope it helps!

Well, on a simple level you might say: You: So, how will this restructuring of the company affect me? Your boss: I'll talk to you about it this afternoon. Talk to = one-sided, will give instruction. Or: You: I am worried about how this restructuring of the company will affect me. Your boss: I will talk with you this afternoon. Talk with = a discussion, two-sided. HOWEVER, the two can be used interchangeably; if somebody says they will talk to you, they probably do not mean that only they will talk and that you will not get to say anything at all. In short, you can use either.

Try not to think about learning grammar as some separate thing. You can learn grammar while learning the language. It really depends on what part of grammar you want to learn, are you able to be more specific? If you are talking about tenses: simple past, present perfect, future perfect, and so on, a good idea would be to look up example sentences of these types (most decent grammar explanations include example sentences). Try, as much as possible, to get working examples of the grammar in action, rather than just trying to memorise rules. It works for most grammar stuff too, aside from tenses. Don't learn the rule for something, find the rule being used, either in a natural context or in a grammar book.

They are all fine, but omit the article 'the' in the first two; just say 'chess' not 'the chess'. They all, more-or-less, describe exactly the same thing. Some people might distinguish 'being fond of' and 'liking', though.