well i am not an expert on these issues.  i am writing these based on my knowledge.  your visa does not matter much.  important thing is, whether you have completed your education in usa or not.  if you have completed your education, then even with valid visa you can not enter usa.  looks like you have not since you are talking about CPT.  you are allowed to work under CPT.  it will be a good idea if you can use CPT during summer starting from period you come back from Nepal.  since you are F1 student with valid visa, you wont have problem coming back with same visa.  however, if you change your status to H1, your f1 will be automatically terminated.  you can not have two status at the same time, that is H1 and F1.