advice, pls, on replacing feeds at 8 months

[duedec2]

Apologies if this is the wrong place for this msg, which is not about introducing solids, but introducing formula. Apologies, too, for the boring name, esp as my baby was born on Nov 21.
I'd like to start weaning my eight-month-old son and would be so grateful for some advice... He currently has four feeds a day: early morning/dawn/earlier-I'm -afraid-too-often; mid-morning (smaller); mid afternoon, and bed time. Is the afternoon one a good one to replace with a bottle and if so, how many mls should I offer? They say 500-600 a day at this age but as I've no idea how much breast milk he's getting or ever has got, that's not a sum I can do. I wonder if it's blx anyway. But in view of the fact I'd like him to fill his tummy healthily during the DAY, how much should I hope for him to drink out of that afternoon bottle? Also, does doing this effect milk supply at other times of the day? Or might it? None of the books I have seem to help me and we are living in India, where there are no health visitors etc.
Thank you so much!