My nearly 5-month old is EBF and have been 'accidental parenting'

by letting him fall asleep on the breast snce birth. We are going to start sleep training to reduce night wakings (currently he wakes up about 4 times a night). However, I'm not sure he doesn't wake up because he is hungry and I want to introduce a bottle so that I can rule out hunger as a cause of waking up. I want to follow Tracy's advice and persist with giving the bottle (I'll use expressed milk) when he's hungry. Now I "tried this, but..." he didn't take the bottle until 3pm (ie he hadn't fed for 9 hours!!!) and even then only had 20ml (then fell asleep exhausted as he normally falls asleep on the boob which he hadn't had, so he was very sleep deprived that day). He only slept for 40 minutes (woke up after his first sleep cycle at which point I would normally feed him again for him to fall back asleep ... You see my problem!!). At 5pm he was getting very cranky - hungry and tired, but as he was still refusing the bottle I caved and put him on the breast. You can imagine the night was worse than ever as he had to make up for the lack of feeding.
Questions: How long do I not breastfeed my baby in order for him to take a bottle? When do I breastfeed him again (and when do I then try the bottle again)? I don't want to starve or dehydrate my baby!!
Thanks for reading!