1)
What is "Yekev Ze'ev"?
1.
Targum Yonasan: It is Meishar Ze'ev. Radak - perhaps the plain was like a Yekev (winepress), with high brims around it.
2.
Radak: It received this name after killing Ze'ev there, and similarly regarding Tzur Orev.
2)
Why does it say va'Yirdefu El Midyan [and not Acharei Midyan or Es Midyan]?
1.
Malbim: Since they seized the water, Midyan were fleeing towards them.
3)
Why was Gid'on in Ever ha'Yarden?
1.
Rashi: He was chasing Zevach and Tzalmuna.