Hindi: is baare meN

Do you hear is baare meN? Example: "is baare meN kyaa khayaal hai?" To me it needs a ke to make it is ke baare meN. Is is baare meN correct?

Yes, both "is baare me" (इस बारे में) and "iske baare me" (इसके बारे में) are fine.

word reference, baare meN

Hindi: maah, maheena

I know that both maah and 'maheena' are used to mean 'month', but is 'maah' more poetic than 'maheenah'?

Though both are used in poems, even I feel 'maah' (माह) is slightly more poetic than maheena (महीना ).

word reference, maah, maheena, माह, महीना

Hindi: piyare miyare dost

Is it alright to say "mere piyare miaare dost" Is this a funny or childish way to say "beloved friend"?

The word "miyare" is not correct. Correct word should be "nyaare" न्यारे or sometimes said as "niyaare" नियारे. "pyaare nyaare" प्यारे न्यारे  is often said to make a rhyme which means beloved. 

word reference: piyare, miyare, nyare, न्यारे, नियारे

tahmad/tahband

Do "tahmad" and "tahband" mean the same? Are these Hindi words?

tahmad/tahband - I don't know their meanings. These are not Hindi words. These sound like Urdu words.

I searched for its meaning in Hindi Khoj disctionary just for reference and it gave blank output too: 

http://dict.hinkhoj.com/words/meaning-of-TAHMAD-in-hindi.html यह शब्द (TAHMAD) अभी हमारे डाटाबेस मे नही है ।
http://dict.hinkhoj.com/words/meaning-of-TAHBAND-in-hindi.html यह शब्द (TAHBAND) अभी हमारे डाटाबेस मे नही है ।

Google says tahband means "belt"; I think we can use बेल्ट or पेटी or मेखला for it in Hindi.

word reference, tahmad, tahband

Hindi: Live as if you were to die tomorrow

Can you please translated in English the following sentences? 

1 जियो जैसे तुम कल मरने वाले हो पढो जसे तुम हमेशा जियोगे
2 जीयो ऐसे की कल मरना हो, सीखो ऐसे जैसे की हमेशा जीना हो
3 ऐसे जियो जैसे कि तुम कल मरने वाले हो और
4 जियो ऐसे ज़ैसे क़ल मरना हो,सीखो ऐसे ज़ैसे क़ि ज़ीवित रहोगे हमेशा ।

1 => Live as if you are going to die tomorrow; study as if you are going to live forever. 
2 => Live as if you are going to die tomorrow; learn as if you are going to live forever.
3 => Live as if you are going to die tomorrow.
4 => Live as if you are going to die tomorrow; learn as if you are going to live forever.

Word reference: jiyo aise ki tum kal marne wale ho; live as if you were to die tomorrow

Hindi: bhednaa vs bedhnaa

Which one do you hear more: bhednaa भेदना or bedhnaa बेधना? Which means "to pierce"?

Both mean same thing and both are heard in the language. 

Word reference, bhedna, bedhnaa, भेदना, बेधना

Hindi: Fill in the blanks

What would be Hindi Translation for "Fill in the blanks"?

You can say, "Rikt sthanon ki purti karen." रिक्त स्थानों की पूर्ति करें।

Hindi: Don't Judge Me

How to say in Hindi: "Don't judge me!"?

One can say, "निर्णायक न बनें". Literal translation would be "आप मेरे बारे में फैसला नहीं कर सकते"; but I would prefer a general statement "निर्णायक न बनें"

Word reference:don't judge me; judgmental, निर्णायक

Hindi: Save Water

How to say "Save water" in Hindi?

One can say, "Paani bachao" पानी बचाओ , or "paani ki bachat karen" पानी की बचत करें

Word reference: save water, पानी बचाओ

Hindi: Two and a half

What is the word for "two and a half" 21/2 in Hindi?

It is called "Dhaai" ढाई ; some times also called अढ़ाई

Word reference: two and a half; 2½; aRhaa'iil; Dhaa'ii; अढ़ाई; ढाई; Dhaai