I’ll start with your questions first as you may need answers for these more than for the other parts of your entry.  The other corrections will just follow.
 

1. “Ibig sabihin kung ano ang ***?” = "Meaning whatever is ***?"

What does *** mean? = Ano ang ibig sabihin ng ***?

2.  “Paano ninyo ito sinasabi sa Tagalog?” = How do you say this in Tagalog?  - Without the “***”, your sentence is perfect.  But if you will insert “***” between “sinasabi” and “sa”, then it will be wrong.  It’s because “ito” (this) is there and it already stands for “***”.  There are 2 ways to resolve this:

a) remove “ito” and replace it with “ang ***”:  Paano ninyo sinasabi ang *** sa Tagalog?

b) keep “ito”, and put “***” after the sentence: Paano ninyo ito sinasabi sa Tagalog?  “***”.

A more standard way of saying it though is, “Paano sabihin sa Tagalog ang ***?”

3. Hindi ko maintindihan, maaari mong ulitin na dahan-dahan?   = "I do not understand, can you repeat slowly?"

I did not understand that, could you repeat it slowly, please? = Hindi ko siya naintindihan, pwede mong (mo bang) ulitin nang dahan-dahan? – "Siya" will mean "it" here even if we use it normally for "he/she".  “Naintindihan” is the past tense.  “Pwede” means the same as “maaari”, but the former is more often used than the latter.  “Mong” is OK in written form because the question mark will show that it's a question.  Orally though, you will hear more of us use “mo bang” instead, "ba" being the question cue.  Native speakers can use "mong" and produce a question through intonation, but in your case, "mo bang" may help you get understood better.    “Nang” is what you use with adverbs, but you need not worry about it here because you will be in conversation and "ng" and "nang" just sound exactly the same.

4.  “Ko lamang na malaman ang kaunti”. = "I only to know a little". – The Tagalog structure for what you wanted to say is different.  Also, “ko” is never used to start a sentence.  It has to be “ako”.

“Kaunti lang/lamang ang alam ko.” = I only know a little.  (You may use "lamang", but I think most of us would use the shorter "lang").

5. I haven't learned about *** yet. = Hindi ko pa natututunan ang tungkol sa ***.  (Correct, except for that additional “tu”.) – An easier way to say it would be to replace “natututunan” (to be learning) with “alam” (know) –> “Hindi ko pa alam ang tungkol sa ***”.  Although with “alam” the sentence can be used to mean knowing about anything and not only what is learned from studying, whatever you put in "***" will make it clear what you are referring to.

kapaki-pakinabang na mga parirala para sa pag-aaral

Gusto kong magkaroon ng  <em>isang</em> <em>pakiki</em>pag-usap sa isang katutubong<em> manana</em>lita, kaya kailangan kong malaman kung papaano sabihin ang mga parilala:

1. What does ________ mean? <em>Anong ibig</em> sabihin ng "________"?
2. How do you say ________ in Tagalog? Paano ninyo ito <em>sasabihin</em> " ______" sa Tagalog?
3. I didn't understand that, could you repeat it slowly, please? Hindi ko maintindihan, maaari mo <em>bang</em> ulitin n<em>g</em> dahan-dahan?
4. I only know a little. Ko lamang na malaman ang kaunti <em>lamang ang aking nalalaman</em> (<em>sa tagalog</em>).
5. I haven't learned about ________ yet. <em>Wala </em>pa<em> akong alam tungkol sa</em> ________.

(continuation)

“Gusto kong magkaroon sa aking unang pag-uusap sa isang katutubong nagsasalita, kaya kailangan kong malaman kung paano sabihin ang mga parilala/pangungusap:” =  I would like to have in my first conversation to a native who is talking, that’s why I need to know how to say the sentences:

“Gusto kong magkaroon” (I’d like to have) needs an object.  It does not have one in your sentence.   “Gusto kong magkaroon ng mga pangungusap na makakatulong...” (I’d like to have some useful/helpful sentences...) may be what you wanted to say.

“Usap” is “talk/converse”.  However, you will encounter it in many forms, like, “mag-usap”, “pag-uusap”, “usapan”, etc.  One of those is “pakikipag-usap”, which refers to the series of verbal exchanges in the conversation.  “Pag-uusap” refers to the conversation as a whole.  Since what you are referring to is how you plan to carry on your conversation with a native speaker, then “pakikipag-usap” is the word that you should use.

I don’t think we have the exact equivalent of “native speaker” in Tagalog.  The dictionary may give you “mananalita” for speaker, but it is used for someone who’s speaking on a podium, for example.  Anyway, since your sentence is about talking with a native, if you’d say “pakikipag-usap sa isang katutubong  Pilipino”, then it would be safe to assume that the person would be a native speaker.

“...kung paano sabihin ang mga pangungusap:” – “Pangungusap” will need a linker to connect it to what follows.  It should therefore be “pangungusap na”.  Better yet, you add “ito” (this; mga ito = these) after it.    

I think this should do it:  

“Gusto kong magkaroon ng mga pangungusap na makakatulong sa aking unang pakikipag-usap sa isang katutubong Pilipino, kaya kailangan kong malaman kung paano sabihin ang mga pangungusap na ito:”  = I’d like to have some helpful sentences in my first conversation with a native Filipino, that’s why I need to know how to say these sentences:”

I’d suggest you give “parirala” a one-way ticket to never-never land.  :-)))

kapaki-pakinabang na mga parirala para sa pag-aaral – This is correct, but it’s something you may only read from a grammar book or hear inside the classroom. I doubt that you’ll ever encounter it in conversations. If you'd ask me what is “useful” in Tagalog, I’d tell you it’s “kapaki-pakinabang”. Would I use the word in conversations? No, not if I can help it, because it’s such a long word. I’d use instead “makatutulong” (actually, more often said as “makakatulong”), which means “helpful”, a synonym for “useful”.

“Parirala” is one of those words I would rather leave inside the classroom. It’s practically a tongue-twister, just like its big boss, “balarila”. I think most of us would say it as “prase” instead. However, what you actually asked for help on are sentences (mga pangungusap), so you can forget about using “pararila” already at this point.

“Mga pangungusap na makatutulong sa pag-aaral (ng Tagalog)”, is most likely how most of us would say it. – “makatutulong” is a modifier of “pangungusap”, so it is better to put them close together. You may also say that as “mga makatutulong na pangungusap”, but the other one sounds better for me. Adding “ng Tagalog” may be optional, but having it there gives clarity to your sentence.

(to be continued)