It's the same as breastfeeding. You feed them as often as they're hungry and as much as they want. You'll probably have a good idea already how many feeds a day he has based on how many times you BF him. That pattern will likely stay roughly the same, though will continue to change over the next few months as he starts to eat more solids and become more active. I would assume he'll need about as many bottles as he already has feeds to start. As for how much, it's a bit of a guessing game and they don't always take the same amount. More than likely at first he'll take less formula than he would breastmilk just because formula doesn't taste as nice, but then it will build up in time. You just sort of have to do some trial and error. Pick an amount to start with - maybe 180-210 ml or even more - and see how much of that he drinks.
If he's finishing it all the time, start offering more. If he's not finishing it all the time, it's probably a good amount for now. There will be waste and there will be bottles that aren't finished, but I always erred on the side of making too much and dumping it down the sink if it wasn't wanted rather than having to go make more in the middle of a feed, which is a hassle. At that age, my daughter was probably haven't about 6-7 bottles a day, maybe 210ml each, give or take a bit.
For the night feeds, you can make them up fresh (some people use the Perfect Prep machine, which makes this easier), make them in advance and store in the fridge to be warmed up, or use the readymade cartons and a clean/sterile bottle (depending on if you sterilise, which I didn't after 6 months). For nighttime, I would pre-make bottles in the evening and put them in the fridge after cooling them in cold water. Then when we needed one, my husband would go get it, warm it up in a bowl of boiled water from the kettle, and then I'd do the feed. It is a bit more of a hassle though and definitely a two man job if you're not using something you keep with you at the bedside. At that age, we had about 1-2 feeds still a night, though during teething it was hourly. A bottle is fine at room temp for 2 hours, so I'd just feed her, set it to the side when she was finished, and when she woke the next hour, we'd continue from the same bottle, getting a fresh one the next time we needed it. That only lasted a few weeks though.
