Hi Socaprice, and welcome to the forum :-)
Since the default maximum allowed rows in the default view in SPS is 100, and since the default view is the one retrieved by InfoPath 100 is what you will get. Its a known issue with InfoPath and AFAIK the only workaround is to set the default view to show all rows (disable paging).
Maybe if you used the lists.asmx web service to retrieve a specific view, you could get around this. Worth trying!
The second issue is quite straight forward:
1.add a rule on your dropdown: for example A is not blank
2.add an action to the rule: Set a Fields Value: B = .
hth
//AndersR