Okay hun. Firstly, yes, you definitely need to be on a 4 hour EASY. On this routine, you would aim for 2 naps of 1.5/2 hours + a catnap. He is in the fifth month now, right?
It is not at all unusual for breast fed babies to go a few days, sometimes even a week between poos. I understand that you are giving him a bottle of formula at BT in the hope that he may sleep longer but it doesn't work that way. And it might affect your supply. Stick to breastfeeding him. It is lighter, easily digestible and it will also help to ease any constipation, which might be caused by the formula you are giving him. I know you want to stick to the feed timings laid out in the 4 hour routine but honestly, many breastfed babies are not able to go so long between feeds. At that age, I would feed on Wu from nap and then offer again right before the nap. If he is hungry, feed him. They do also get very efficient and are done nursing super fast at around that time. Could he be teething? You mention him not sucking but just holding the nipple..
I'm happy that you have a concrete plan in place and DH will be around to help. But you have just said that he is able to settle himself to sleep when PD drowsy. That is fantastic and you now need to build on this skill by being consistent in your routine and PD.
Just start fresh. Pick a fixed wu time. Plan your wind down routine. PD drowsy but awake and let him learn to settle. Try to resettle short naps using wake to sleep, hold through the jolts etc. After a short nap, reduce your next A by 10-15 minutes and PD again. It won't be easy but consistency is key. Listen to your baby, use this time to observe him, keep a log of his day. And remember that this too shall pass. You are teaching him how to sleep and although it won't be easy, it will help him for the rest of his life. You can do this. Hugs!