As has been said many times, they did originally intend to spread their forces throughout the system and open with negotiations. When that failed, they would cripple the UEF forces from the inside out with minimal bloodshed, having taken up positions in strategic locations.
Two things happened as a direct result of the Vishnan intervention: 1) The forces arrived late in Sol, giving the UEF time to prepare after (IIRC) detecting unusual subspace activity at the newly-reestablished Sol gate, and 2) The ordeal suffered by everyone in the fleet, especially meeting the Sanctuary, convinced some of them that they couldn't wage a war against their own people. Admiral Bei and Captain Bei's wing defected outright, as did the Sanctuary (obviously) and IIRC that one Anemoi, and a bunch of other ships were crippled as defectors fought against GTVA loyalists.
[EDIT] I got some of this right and some of it wrong but read "The Reunion" in the species.tbl it says everything
