1) You should not submit the application without a medical - this should only be done for a "within Canada" application, which yours is not. They try to process dependent child applications quickly and, if you submit without the medical, it's only going to delay processing.
2) Could you provide a link or name/number of the specific form you are referring to, please?
3) Yes, if you are the father.
4) Yes, you can get the medical done in that country. Use
this Designated Medical Practioner website to find a DMP in the area where he is visiting.
5) Some of the forms in the Spouse/Partner/Dependent child application kit will not be applicable to a child sponsorship, such as the Spouse/Common-law Partner Questionnaire.
6) Whether or not you need a notarized copy of the birth certificate will depend on the specific instructions included in the Document Checklist (Appendix A) of the Region Specific forms for the area of which your son is a national. Since you haven't mentioned where that is, I can't tell you specifically. Also, depending on how long a visit your child has been authorized in the country he is in now, he may be able to apply through that country's visa office, so you might want to provide that info, also, and we can help.