The routine we had was pretty similar to the one in Gina Ford's book (but with an extra feed and slightly more daytime sleep). Before using a sleep consultant, I was giving extra feeds during the day for the same reason as you and was very skeptical about restricting feeds when the sleep consultant advised me to. I reluctantly agreed to try the reduced number of feeds for a week with the intention of increasing the frequency as soon as the week was up but it worked wonderfully and she didn't go hungry at all. She explained it to me that by me feeding her frequently and letting her doze on the breast (she would doze with feeds but refuse to nap all day), she was constantly snacking and not taking a proper feed to fill her up. She said that if we have a day of grazing without proper meals, we also don't feel full and sleep well, its even more applicable in their case as they are growing.
In terms of distinguishing hunger and habit - it was the sleep consultant who told me to apply the 4 hour rule. If she woke within 4 hours of a feed, I was to use PUPD and put her to sleep. If the technique took so long to get her to sleep that it ran over 4 hours, I was still to continue and get her to sleep then feed her when she next woke up (I never needed to resort to this but she said it was an important point to avoid them learning to resist sleep for a certain timeframe before we give in and feed). Within 2 weeks she was sleeping a 6-8 hour stretch after being put down at night and then a further 4-5 hours after her feed.
Prior to the 4 month regression, my daughter used to sleep through the night at her own accord but be awake all day so an 8 hour stretch at night is certainly possible for your one. At around 17-18 weeks, regression hit and everything fell apart as she already didn't nap and poor night sleep resulted in a very grumpy and overtired baby. We did attempt PUPD on our own but with partial success.
I personally think its a good idea for you to have an established settling technique before your one hits the 4 month regression so you know how to settle him and he knows what you want him to do when those wake ups become more frequent. Its definitely what I intend to do if and when I have another baby to avoid having any of the sleep disasters I had with my daughter
(Also with regards to your health visitors comments about supply, you have successfully established breastfeeding so if you are ebf and baby is growing normally, you will have no supply issues if baby sleeps long stretches at night. As I said, mine slept 8-10 hours at night from 8 weeks old until she was 17ish weeks, then again from around 22 weeks and I am still happily breastfeeding at almost 11 months)