1. have you tried a clientless attack?
2. Of course range effects the injection process. most WEP is crackable in under five mins.
just because there is no encryption does not make it public. If you do not have permission from the owner then it is still illegal.There is a public (without password) AP in my vicinity
4. as for several .cap files you have the syntax already!! it would be
to use all .cap files in the pwd orCode:aircrack-ng -b 00:11:22:33:44:55 *.cap
to use only cap files of that nameCode:aircrack-ng -s -b 00:11:22:33:44:55 filename*.cap