To get the size and RVA of the directory entries you can iterate through them with the list in the Optional Header:
The following snippet will return a list of pairs (Size, RVA) for each of the directories:
[ (d.Size, hex(d.VirtualAddress)) for d in pe.OPTIONAL_HEADER.DATA_DIRECTORY ]
To iterate thought the actual imports:
for entry in pe.DIRECTORY_ENTRY_IMPORT:
print entry.dll
for imp in entry.imports:
print '\t', hex(imp.address), imp.name