At this time of year I would wean, even if it was early. There is no advantage to the foal to be on the mare, dragging her down, as all the goodness goes from the grass and her milk suffers. It is far better to have the foal off the mare and eating a good feed twice a day, better for the mare and the foal both.
Now all this is assuming the foal has been fed before weaning, properly, and is in good condition.
I do not think you need to do anything special at this stage- since the foal is weaned giving it milk pellets will not really help as the digestive proteins in the system will have changed and it will not be able to digest milk properly. It is a modern myth that adult animals benefit from milk- they cannot digest it really- your money would be better spent on assuming the foal has not been as carefully fed as you would do (you may be pleasantly surprised, though) and investing in a good, higher protein, foal/weanling feed.
I would suspend any criticism until you actually get the foal home and see what condition it is in.
I always breed my mares back on the foal or next heat. It is only at this time of year, with a late foal, that I have ever had a mare look a little tired.
As to weaning age, I pretty much leave that to the mare...I do not wean, whatever, under normal circumstances, until the youngest foal in the group I am weaning, is four and a half months old, and then only if the mare and foal are ready.
