good research requires knowledge of history and geography especially in countries where war moved borders, and people, where names changed when conquering countries took over. go to ukraine board and read other peoples queries and replies to help u in your search. e.g. in 1881 jews fled odessa for brody (from the net) -something like this could be critical to your search.
also, u note that sarah spoke german-note-
In 1763, Catherine II (Catherine the Great, German born empress of Russia) sent agents into the German states for the purpose of recruiting settlers. These colonists were to develop the fertile, uncultivated agricultural lands southeast of Moscow, specifically along the VOLGA River. There were several promises that made this offer attractive to the Germans: freedom from various forms of taxes and customs duties, self government for the towns, freedom of religion, and freedom from military service, to name a few. It is easy to see how attractive this would be to Germans who were suffering from widespread poverty, malnutrition, and unemployment brought on by feudal infighting, wars, religious persecution, and the general politics of the day. The extent of this migration was so great (4000 families in 1767 alone) that further migration was forbidden by the German Emperor Joseph II. Migration to the VOLGA effectively ended at this time. During these 4 years it is estimated that over 25,000 Germans migrated primarily from Hesse and the southwest states but nominally from other areas as well.

In the next few years, Catherine the Great expanded Russian territory dramatically by conquering Turkish controlled land to the south and Polish land to the west. Catherine again wanted Germans to help in developing her new territories, especially around the north side of the BLACK SEA. This time she turned to the Mennonites of West Prussia. Mennonites are a pacifist denomination. Frederick William II was demanding payment of heavy fines in lieu of military service and forced the Mennonites to pay tithes to the established Lutheran Church on earlier land purchases from Lutherans. They were particularly attracted to Russia by the offer of freedom from military service. In 1789, 228 Mennonite families arrived at Chortitza on the Dnieper River. They had been preceeded to the general region by a smaller group of Lutherans. The Mennonite migration continued into the area for another 80 years with thousands more families answering the call. Thousands of other Germans followed the Mennonites. Lutherans and Catholics began flooding into the area, starting particular after the Napoleonic wars (1803 through 1810). They not only came from the southwest German states but also from West Prussia, Hungary, and Poland. Hundreds of German colonies sprang up in a semi circle around Odessa, now in the UKRAINE
this is from www.genealogienetz.de/reg/ESE/russia.html
which has lots more to help u
try this
UKR-ODESSA-GEN. A mailing list for research, discussion, and sharing of information regarding Jewish genealogical questions, family research and existing information about the past Jewish communities of the city of Odessa, Russia (now Ukraine). To subscribe send "subscribe" to ukr-odessa-gen-l-request@rootsweb.com (mail mode) or ukr-odessa-gen-d-request@rootsweb.com (digest mode).
google odessa russia genealogy non in quotes for much more, then odessa jews for this http://www.shtetlinks.jewishgen.org/odessa/sitemap.htm and many more
odessa jewish genealogy turned up more incld
http://www.bh.org.il/Exhibitions/Odessa/community.asp which was a huge source of additional places to search
this should get u started
good luck!!