asifiq

No it's not a problem...u can upload it

If there's no document on vaccinations at the time of filling the form, check "NO" and on the field for more information state you'll get it at a later date when the medical is performed. 
 
Medical examinations abroad are performed AFTER filling the form, a few days before the actual interview; that's when the documentation to establish that you have received vaccinations in accordance with U.S. law will be generated.

Then it is No

Correct. At the visa interview the CO will start adjudicating the IV application. The CO will add/annotate things and the updated answer to the relevant question will reflect what is stated on the DS-3025.

Actually, from next month (May 2019) onward you should be expecting to to be contacted by NVC to assemble and submit required documents to them based on "B.  DATES FOR FILING FAMILY-SPONSORED VISA APPLICATIONS" even though your priority date won't be current just yet based on "A.  FINAL ACTION DATES FOR FAMILY-SPONSORED PREFERENCE CASES". 
https://travel.state.gov/content/travel/en/legal/visa-law0/visa-bulletin/2019/visa-bulletin-for-may-2019.html
 
If I were you I will contact NVC now to make sure they have both the Petitioner and Beneficiary's current email address on file in anticipation of correspondence from them on how to proceed. 
If you want to start familiarizing yourself with what the NVC process involves, check the link below:
https://travel.state.gov/content/travel/en/us-visas/immigrate/the-immigrant-visa-process/after-petition-approved/begin-nat-visa-center.html
 
Good luck.