1)
What is the meaning of "Simneh... k'Chayil ha'Nofel"?
1.
Radak: Add soldiers like the number who died, so there will be the same number as last time. Malbim - there is no need to add!
2)
What is the meaning of "Im Lo Nechezak Mehem"?
1.
Rashi: You will see, [if you will have the same size army as the first time] if we will not overpower them.