I agree...I would not be adding another female Rottweiler to your home. Two Rottweiler females, once mature may not get along. May even want to kill one another.
Are you prepared to keep them separated for the rest of their life...if things don't work out between them?
Please read this thread:
ttp://www.rottweiler.net/forums/behavior/43753-bitch-fights-raising-two-adult-bitches.html
As far as walking...dogs must be conditioned to walk for longer distances...not fair to the dog to walk 30 minutes a day during the week, and then take the dog out for a two hour walk on a weekend. Start doing longer walks during the week....walking up hills...and condition the dog for longer distances.
Gina