4)  What can we learn from MS textual and iconographic analysis, and how is that typically described and used?

If your text is religious (highly likely!) it probably reproduces ritual language that has been recorded elsewhere from MS transcriptions and in printed liturgical texts.  Once you can read even a little of your text, look for them elsewhere using Google's "exact search" form (i.e., using those quotes would search only for those characters "exact search" between the quotes, in that order).  Practice will teach you to seek the most idiosyncratic phrases, ideally short ones, that will produce reliable results.  Some short formulas are so ubiquitous as to be useless (e.g., dixit dominus, "said the Lord").  Also, beware the abbreviation of commonly used words and phrases (e.g., dm for "dominus").

Text and image are intended to work together--if you identify one, it will help lead you to the other.  Especially in horae (books of hours), the typical pattern of texts and typical pattern of illuminated miniatures tend to be highly predictable.  See Wieck for more detailed guidance.  If you have an horae calendar leaf, which looks like an Excel spreadsheet with a month title at the top, left columns for days and right columns for saints and other persons who are given feast days/prayers, you can sometimes identify the region of origin by which persons are accorded feast days.  Famously, Thomas a Becket and Edmund Martyr are found in all "Sarum Use" horae (those which followed the rituals of Salisbury Cathedral, like the Berners Hours).  Other regions had their own most favored saints.

Illuminations are (often, if religious) formulaic in structure and are intended to be "read" for their attributes.  Saints are common subjects of miniatures, and each saint comes with identifiable attributes.  For instance, a female standing with a palm in her hand, the other hand resting on a wheel (perhaps broken), is St. Catherine, whose martyrdom (the palm) involved an attempt to torture her with a horrible wheel, which God broke into pieces.  St. Margaret resisted demonic temptation until Satan, himself, appeared in the form of a dragon and swallowed her, but the Crucifix she held broke the demonic power and she burst out of the dragon, usually while it was still in the process of stuffing down the train of her blue dress.  The Hours of the Virgin always begin with The Annunciation, at least if the leaf survives, and she always receives John the Baptist's mother in The Visitation, during which the in-utero John recognizes the in-utero Jesus and kicks mom.  The Passion and Crucifixion, which structure the Hours of the Holy Cross, similarly have their own repeated iconography.  Such scenes were intended to inspire rapt, focused meditative attention, often while uttering appropriate prayers that centered the mind on specific spiritual goals.

Texts are (often, if religious) formulaic in content and are intended to be "read" as recitation to bring the mind and spirit into harmony with God, Christ, Mary, the Saints, and Sacred Events the worshiper hopes to experience directly through this performance.  At least since the era of St. Augustine's (354-430 CE) Confessions (397-400 CE) and On the City of God against the Pagans (ca. 400), Christian worship practices have used texts and images to refocus worshipers minds away from the present moment and place, and toward the Divine, its own time and place outside the present.  Augustine anchors his readers' approach to worship with a description of his moment of conversion from secular philosophy, hearing a child singing "tolle, lege" (take [it], read [it]) which led to his sudden seizure of Paul's Gospel and his timely reception of the passage his eye fell upon (Epistle to the Romans 13: 13-14).  The book spoke to him and through him to his readers, telling them not only what to do (abandon earthly desires, seek Salvation through Jesus) but how to do it--read intensely and meditate on what you are doing, break the cycle of ordinary reasoning and find the extraordinary world of Revelation.  Using reason to reach beyond reason is a tough lesson, but worshipers' repeated exposure to the annual cycle of sacred events and persons was intended to break down the secular "will to understand," to replace it with Understanding that comes from outside via the MS they are holding and the images they are contemplating.  In the C14-15, Thomas a Kempis' Imitatio Christi (Imitation of Christ, ca. 1441) gave worshipers an even simpler formula for breaking through to the Divine.  Meditate intensely on the suffering of the Passion and the Crucifixion, be one with the suffering God, and surrender to the images and recited prayers until they move one beyond the place and time of worship.  The coincidence of Thomas' work's immense popularity and the rise of the horae in the C15-16 is no coincidence. 

If you are looking at a single horae leaf, was it recently removed from a binding (clean edge facing the sewing and a clean razor-cut), or was it removed long ago to serve as an aid to worship (darkening on both margins, perforation[s] at corners or top]?  Images of worshipers from the late C14-16 often show them in rooms with a wall decorated with a single slightly curling leaf containing an image and some text.  Those are likely horae leaves that have been removed their bindings and pined to the wall to create personal shrines.  This imitates the great cathedral frescos and panel paintings to focus the meditative minds of whole communities in group worship.  Look for puncture marks in the top margin and in the corners.  These leaves do not often survive intact, however, being "worshipped to death."  Many a whole horae suffered the same fate.  The only horae that survive in their "pristine" forms are those that were never or only rarely used by their owners, or that entered collectors' hands soon after their creation, perhaps because of the owners' premature death.

If you are looking at a legal or theological text, pay close attention to the patterns of marginal staining and of interaction between readers' marginalia and the main scribal text.  Readers leave numerous concrete signs of the places their attention was most focused, either in approval of or debate with the text.  Catherine Rudy has demonstrated that scientific measurement of the dirt/oil deposits on leaf margins throughout a MS will vary widely and can be used as an index of a given passage's popularity with generations of users.  Layers of annotation are even more readily interpretable as indices of the kind, as well as the intensity, of readers' attention.

Once you have reached the level of textual and iconographic analysis, it often pays to take a break and retreat to asking the more basic, global questions with which you began.