Geof,

Like others have said, under the circumstances you now find yourself in, at least you seem willing to stand to the mark.

I will do my best to give some suggestions, but in reality it's outside my scope of experience. So please accept with the spirit with which it's given.

From the information you have given, there already appears to be some warning signs, I feel that you recognise this yourself from the way in which you have raised your questions.

What expenses can i pay directly?

The child is still really quite young and the short term needs would most likely be food, (milk etc) clothing (remember that babies grow so fast).
I can't think that there are any expenses here that you could pay directly. Unless the mother is willing and able to provide itemised receipts. (may not be good to ask?)
I believe there would need to be some trust between you if you will continue to send cash.
An alternative could be that you send food and clothing to the mother via a Balikbayan Box. This would need to be on a regular basis. This would likely be more expensive than the equivalent costs in Phils, but at least it's direct contribution.
As the child gets older this way would become more difficult.

You will need to use some common sense for costs as the child gets older. Keeping in mind the average income is OK up to a point (for everyday things) but often medicines and medical treatments can be very expensive. Just be aware. It is possible to get receipts for this, but how will you react if the mother says she forgot? You may need to contact hospitals direct.

I feel it's going to be a difficult for you to keep a level head when you are asked for large sums for the sake of your son! (despite your best intentions) and you will find your heart rules your head.

Health Insurance would be a very good idea. At least you will have a fairly secure way to check on the actual costs of any treatments/ services.
There is some very good information on recent posts on this forum. Please do some searching.
Philhealth is the govt scheme and runs at about P100 per month So a very small cost.
I believe this covers 40% - 50% of medical costs.
Education will need to be paid for.
When the time comes you should be able to have some inputs into the actual school. Payments will be relatively easy to be made direct to the school. Books, uniforms etc
can be paid to the mother. The school will tell you whats needed and the estimated costs.

Regarding trust funds etc. I leave to others to make suggestions


I would only add, that please also consider the needs of the mother. She will likely be the one who is providing the love, care time and attention on a daily basis. It's not solely about the child.

I feel sure this thread will continue with lots of good advice. You came to the right place as this forum has plenty of good people all willing to help and support and all very active on this site.