Why do composers find string instruments (such as violin) so compelling to write solo pieces for, in the absence of harmony?

Because it does have harmony in place: Double stop.

Now: how many solo pieces are there for brass or woodwind instruments? And how many of them are as renowned as the solo pieces for strings (including plucked strings)?

I think you have your answer.

What non-Roman scripts keep foreign words in Roman?

In the last few decades, written Greek uses Roman script for foreign names by default, unless the name is extremely newsworthy. So you’ll see

Το συγκινητικό ντοκιμαντέρ για τη ζωή της Amy Winehouse (The moving documentary on Amy Winehouse’s life)

Rehab της Amy Winehouse, σε διασκευή των Vocal Adrenaline. (Rehab by Amy Winehouse, arranged by Vocal Adrenaline)

More rarely, you’ll get Roman + Greek:

Ο πατέρας της, Μίτσελ Γουάινχάους (Mitchell Winehouse) ήταν ταξιτζής και τζαζίστας, η μητέρα της Τζάνις (Janis Winehouse) ήταν φαρμακοποιός (Her father Mitchell Winehouse was a cab driver and jazzman, her mother Janis was a pharmacist)

And rarely (I find), you’ll get just Greek:

Η Έιμι Γουάινχαουζ «ζωντανεύει» δια χειρος Ασίφ Καπάντια  (Amy Winehouse comes alive through the work of Asif Kapadia)

This doesn’t get done for world leaders who show up in newspaper headlines constantly. So Schäuble, the German finance minister and current bête noire of  Greece, is always transliterated as Σόιμπλε. The headline in the following is more unusual than the lead;

Κρεμλίνο: Ο Putin δεν θα συναντηθεί με τον Εrdogan (Kremlin: Putin will not meet Erdoğan)

Ο Πρόεδρος της Ρωσίας Βλαντίμιρ Πούτιν δεν σχεδιάζει να συναντήσει τον τούρκο ομόλογό του Ρετζέπ Ταγίπ Ερντογάν … (The president of Russia Vladimir Putin does not plan to meet with his Turkish counterpart Recep Tayyip Erdogan)

The foreign script is always Roman; you won’t see  Ο Путин δεν θα συναντηθεί (even though Cyrillic should be more familiar).

Of course, there is individual variation. In this Reddit thread (Τι κάνει ο Χόκινγκ; Επιστήμη ή μάρκετινγκ; (Το άρθρο που “καίει” αυτή τη στιγμή το twitter #protagon_science) • /r/greece), the first comment has Χόκιγκ, the second has Hawking. 

The untransliterated Roman is a recent thing, maybe two decades old. Before then, transliteration into Greek was universal.

What is the meaning and origin of “kapeesh”?

I presume you’re referring to the Italian-American word capisce. To my astonishment, Urban Dictionary’s entry is not half bad:

Capisce

Capisce (pronounced cah-PEESH) is an Italian word that is used in American slang to say “got it” or “understand.” The correct word in Italian would be capisci (pronounced cah-PEE-shee) to address the second person informally, a.k.a. you.  

(I’m presuming the dropping of the final vowel is Italian dialect.)

History: During Alexander’s invasions, would his soldiers have found Old Persian or Indic to be somewhat familiar sounding given their closeness to Greek?

Good insight, Sabeshan. Probably.  And they probably wouldn’t have cared.

300 BC was a good time to be doing historical linguistics. The Indo-European languages were a lot closer to each other back then than they are now. In fact, the only reason Indo-European was discovered and reconstructed when it was, was that we had 2000 and 3000 year old records of Indo-European languages.

And the Greeks were well placed to do historical linguistics. They were already familiar with lots of different dialects of Greek, and the regular phonological correspondences between them.

But the Greeks did not make much of  historical linguistics.

  • For starters, they didn’t really have the wherewithal for linguistic analysis. Linguistics as we know it is a Roman-era invention. The sophists got language analysis started in Classical time, but it was quite rudimentary. Aristophanes in his Frogs makes fun of Euripides’ new-fangled, sophist-inspired notions. Those notions include word and verse.
  • For seconds, they were profoundly indifferent to the barbarians’ languages. They were, after all, bar-bar-bar gibberish. Herodotus records some Persian and Scythian derivations of names, so Greeks did learn languages; but they didn’t at the time particularly reflect on them. I think some Greek somewhere did speculate on Latin being a Greek dialect, because of the similarities; but that was later.
  • For thirds, reflecting on the relatedness of languages is a very recent thing. The identification of Indo-European and Uralic languages as families is a very late thing—18th century.
  • For fourths, if all the languages you’ve been exposed to are Indo-European, then your conclusion is that all languages  in the world have vaguely similar words for “mother” and “daughter”. Someone who particularly cared could have noticed that those similarities did not extend to Phoenecian, Egyptian and Aramaic (or even that Phoenecian, Egyptian and Aramaic were similar). The Greeks did not particularly care.

Does Bach’s Chaconne in D Minor sound better in other transcriptions than the original composition on violin?

IMO no. Part of the emotional point of the Chaconne for me is that it sounds hard to play. Keyboard versions in particular don’t register with me. (No, I haven’t heard the Busoni yet.) I’m a bit more ok with Lute/Guitar versions, they sound more idiomatic.

Classical Music: Does everyone play the same notes in the orchestra while playing a symphony, or do composers write different notes for each instrument in the orchestra while creating their music?

Almost always different notes. Even Unison  passages mean that different instruments play the same note in different octaves.

Exceptions are so rare that this is the only one I can think of (though there are bound to be others). In Berg’s opera Wozzeck, right after Wozzeck kills Marie, Berg has an “Invention on a Single Note”. This has the note B played twice. The second time is in unison, with every instrument playing it in different octaves, in a long, terrifying crescendo.

The first time is usually played shorter, but I consider it even scarier. It is every instrument, one joining in after the other, playing the same note at the same pitch, B under middle C.