Pakistan is indeed a big country. There are fout provinces in Pakistan. The souther part of Pakistan although can be visited year round but during summer (May to September) is rather hot and you will need to travel long distances and car or vehicle must have airconditions.
The Northern Pakistan is partly closed during winters but is ideally best to visit between March to November.
Here are some basic tours one can plan to do on a tour of Pakistan this year i.e April to December