Hi,
DS-160 - This was the first thing that we did when doing the K2-Follow to Join process. So, it would be okay to start this process now.
Visa Payment - Once you complete the DS-160, you can do the payment process. There are several payment options to choose from. Choose your most convenient option. Keep your receipts
Interview Scheduling - Once you pay, you should start attempting to schedule the interview. It's probably not a bad idea to start this process now since interview slots may be limited. Check early (Philippines time) and often
Medical appointment - see details here (https://slec.ph/registration/us/visa-applicant.php). You will need to time it correctly and your timing in your post is good. You will need interview appointment printout, your DS-160 confirmation page, Special Power of Attorney document allowing someone (guardian) to travel with the child and grant permission for the medical exam, the guardian's ID (passport), a copy of your passport, vaccination record, etc. See the link above for more details because my document list is not complete.
Other info - A nice hotel is helpful because your appointments will probably be early. The City Garden Suites Hotel was the one we chose. It is very close to the medical and relatively close to the Embassy.
Interview - You will need similar documents for the interview plus a whole lot more.
I hope this is helpful. If you need to reach out with more specific questions, feel free to respond to the post or contact me directly.
Scott