What are the halachic issues/opinions/options regarding starting work early, i.e. before one is allowed or practically able to daven Shachris?
See Rabbi Gil Student, Shacharis Tips of the Unemployed, Hirhurim:
I. Earliest Times for Shacharis
The general rule is that Shacharis can only be prayed (at or) after sunrise (Shulchan Arukh, Orach Chaim 89:1), ... Bedi'eved, if you prayed after dawn, you fulfilled your obligation. But really you are supposed to wait until after sunrise. (Dawn is calculated differently by different authorities.) ....
However, someone who has to leave on a trip before sunrise is allowed to pray in that period between dawn and sunrise (Shulchan Arukh, Orach Chaim 89:8). Contemporary authorities categorize a commute to work as a trip for these purposes, and when I was commuting to yeshiva from Brooklyn to Washington Heights I was told by my rosh yeshiva that this was also sufficient reason for praying before sunrise.
In New York, during much of the year, dawn is between 4:15-4:30am (although at times, it does get close to 6:00am). If one does start work before dawn, it would be permitted to work until dawn. However, one is not allowed to do work-like activities after dawn if one has not yet prayed (see Tefillah Ke-Hilkhasah, ch. 6 and Law of Daily Living vol. 1, ch. 11).
One exception discussed by Rabbi Student would be if one has a set minyan. He also discusses dissenting opinions that do not allow for this exception. One might therefore surmise according to the lenient position that someone could start work at 4:00am today if he has a set minyan at 10:00am (prior to the conclusion of the time for prayer, or, forgoing timely prayer, until midday).
For zmanim in your area, please see MyZmanim.com.
Of course, if you're confronted with this situation in practice, you should consult your Rabbi to determine what to do.