Good place to use Min/Maj 7 Chord

I finally found a good place to put this chord, and I know why ^^.

Yep, that's the point of theory - you know the why. And the point of studying theory (for those who say you don't need it) is to experience things like the m/maj7 in the first place - that makes you ask the question, find the why, and expand your musical vocabulary :)

Hmm I wonder.. is there any specific way to write different voicings of chords ?

Not like inversions, but different voicings of chords, same notes, same order and everything, but different strings, any way to specify that when writing out the chord, I know in sheet music you write Pos I or V etc etc, but what about when writing the chords ?

Different notation systems convey different information.

Rhythm charts (chord symbols) tell you what the harmony is; by using 'slash' chords you can specify an inversion... but the exact voicing is up to the performer. The reason rhythm charts are used more than standard notation for pop music is that you don't need to worry about the instrumentation or arrange the piece in advance - you're leaving the exact voicing up to the musician's ears. If you're looking at a C7 chord, you might play a full barre if you're solo, a four-string voicing if you're in a drum/bass/piano situation, a different four-string voicing if you're in a different quartet, or a two-string E/Bb interval if you're in a big band. Unless you're writing an arrangement for a specific ensemble, rhythm charts are a great option.

Tab specifies a fingering; implicit in that is the exact inversion - if you want pitches (low to high) A-F#-A-D, you could tab x0423x.

Standard notation lets you specify the pitches, but generally lets you leave the fingering up to the performer. The same pitches might be realized as x0423x - but the performer might also do 5977xx and get the same result. Using a position number narrows the choices, but specifying "Pos II" for those notes might be realized as x0423x or 5x423x. If you want to be as specific about a fingering as tab, you use string numbers - a number inside a circle placed under or over a note tells you exactly where it should be played.

There are other systems too, like figured bass - that gives you a bass note and numbers telling you how many diatonic steps above the bass the other notes are. The bass specifies the inversion, and the numbers build the chord - if you want Em with G in the bass, you'd have a G note (in standard notation) with '36' written above it; that tells you to play a third above the G (B) and a sixth above the G (E). Since the bass is pitch specific, that's more specific than a rhythm chart - Em/G lets you pick which G note to use as the bass, figured bass doesn't. (Figured bass lets you write any chord - if you were in the key of F, the same notation gets you Eº - because the B is flatted by the key signature; if you wanted Em, you'd write b36, and you'd still get Em)

All notation systems try to strike a balance between giving information and being easy to read. The more information you include, the harder it is to read. Systems that are hard to learn (standard notation) can convey just about anything. Systems that are easy to decipher (rhythm charts) have to give less information. IMO you can also give TOO much information - tab (or standard notation loaded with string/finger numbers) doesn't improve the realization of music. Any art that's meant to be created in time, like music or drama or performance art, is a collaboration between a creator and an interpreter.

A play uses a script with the exact words to be used, but the actor and director shape the delivery to make the piece complete - you won't see a script with instructions like "emphasize the third syllable" or "say this word more softly". Doing that implies the actor and director have nothing valuable to add to the interpretation. In stuff I write, I'd rather see what other people can add to it, so I'll be as general as I can - I'd rather use "moderato" than "MM=116", and unless something might be confusing in how it can be realized (like the G#/A xx62xx example I used in another thread with you), I won't use finger/string numbers in standard notation.