We need to sort a few things out here.
First, we are dealing with a confusion of classical theory usage and the naming conventions of chord symbols (which were originally developed by guitarist and ukulelelelelists).
For the chord symbols, the "sus 4" and "sus 2" (which is sometimes written as "add 2") are naming conventions to describe a certain combination of notes and are only tentatively related to the classical theory usage. In a triad, both instances represent a replacement of the chord third by either the 4th or 2nd scale-step above the root. A C major triad is [C E G]. If the E is replaced with F [C F G], it becomes a C sus4; if replaced by D [C D G] it becomes a C sus2. In the case of 7th chords, you would rarely encounter a "7 sus2" since the 2 is equivalent to the 9 (although the 2 does imply replacing the third while the 9 implies the presence of the third.) As far as the "7 sus4", that occurs frequently, particularly in lead sheets that do not indicate anything beyond a 7th chord. It is functionally practically identical to "x11". Although, the "11" implies the presence of the both the 9th and the 3rd and the "4" says little about the 9th and implies a replacement of the 3rd by the 4th, in general usage, the 3rd is frequently omitted in voicings since it creates the very dissonant m 9th interval.
Though I have seen it, a "min sus4" or "min sus2" (whether triad or 7th) does not really exist since the characteristic note (the minor 3rd) is missing. Its only possible practical purpose is that it warns one that the following "chord of resolution" is going to be built on a minor triad as opposed to a major triad. If the 3rd were added in, then these would be functionally identical to the "min 11" and a "min 9". In the case of a "min 11" it is generally voiced with the 3rd since there is no major problem with the interval between the 3rd and the 11th and without it, it is functionally identical to a dominant 11.
When working with these chords in the context of chord symbol, it is best to just consider them as an indication of how the notes are combined to form them, since as often as not they do not follow the classical context of "suspension."
Now, the name "suspension" and its derivatives comes from classical usage meaning "suspended resolution". A classical suspension is a three step process -- preparation, suspension, resolution. First the note to be suspended is introduced as an essential member of the harmony -- chord tones [1 3 5] and in the case of the dominant 7 [1 3 5 7] (Note, some books will say "consonant" to the harmony, but this is not necessarily true in the case of a dominant chord since the 7th is dissonant. But the 7th has been considered an essential part of the dominant 7th for centuries). Then when the chord changes to the next harmony, a note (or notes) that is (are) dissonant -- not an essential member of the harmony -- is maintained over the other notes of the new harmony. Finally, the suspended note is resolved to a note that is consonant and an essential chord tone. The resolution is by step usually descending. Also, in all instances except when the suspended interval is a 2nd, the upper note is the note of resolution. If the interval is a 2nd, then the lower note descends.
Rhythmically, a suspension "crosses the bar". Though the bar line may not actually be present, the preparation and resolution falls on a rhythmically weaker beat or portion of a beat than the actual suspension. In its most basic form you would have P |S R || (P = preparation, S = suspension, R = resolution.
Let's try first a progression IV - I with a suspension. In C major:
IV F / C F A
Isus C / C F G
I C / C E G
The suspension is "prepared" by the R.H. "F",an essential tone, and in this case consonant, of the F major triad. The "F" over the "C" in the second chord is the suspension. It creates two dissonant intervals -- P4 above "C" (which is considered harmonically dissonant when the lower member is the bass) and a maj 2nd between F and G.
Finally, the suspension is resolved when the "F" descends a half step to "E", an essential consonant interval.
Classical suspensions are classed by the intervals of the suspension and resolution above the bass. Thus, the above is a "4 - 3" suspension. Others are the "7 - 8", "9 - 8" and the "6 - 5". You may say that in the "6 - 5" that the "6" is consonant with the bass. In this case, the 6th is less stable than the 5th and is not an essential part of the final harmony.
