Hi there and welcome
Pu/pd is really a method for smaller babies, and those who cannot stand up and down by themselves. Assuming that your 14 mo can do this, and seeing that he is not and hasn't been an independent sleeper previously, I do think gradual withdrawal is your best bet. The two methods used to sleep train toddlers that we would recommend are GW and walk in/walk out. The second of these works better for LOs who have already learned to self settle but need to get back to it after a glitch or illness of some kind.
Have you seen this link:
Walk In/Walk Out vs. The Gradual Withdrawal Method (HOW TO CHOOSE)It helps explain the differences in the methods and why we recommend GW for you.
So that's the St bit, and you can always try to sleep train whenever you feel ready. It is worth bearing in mind that at this he there will probably be crying inveaolved because he is protesting the change from the ways you have always helped him sleep, but as long as you stay with him while he cries (or eventually reassure with your voice from outside of the room) the bond of trust between you will not be broken. If you find listening to his cries difficult (as I have always done with my DD) you could try some earplugs. They will help to take the edge off the harsh frequencies of the crying and they certainly helped me cope better.
I warn you of this as I think itms good to know that it could be a hard process for you, but as long as you are committed and consistent and don't give in, it will get better over time
and we'll be here to support.
As for the routine, it does look like you are part way through dropping that CN and moving to one nap. My DD did this at a similar age. Anther useful thread to read to see how others cope with this 2-1 nap dropping phase is here:
From 2 to 1 nap transition (10-12m and older)It seems like you have been following the longer am nap shorter pm nap pattern and that for a while this has been working. Those wakings at night do seem to be in part UT (undertiredness). Chatty wakings followed by crying are often UT but with the LO becoming OT (overtired) as a result leading to lots of wakings. The lack of self settling will also make it harder for you all as he needs you to get back to sleep.
Don't worry about the accidental parenting you've done so far, there are many of us here who have used AP to get us through, and being a parent is so so tiring, when you're this tired of course taking a child into bed and all goon back to sleep is the good option in the immediate moment.
You might find pushing towards just one nap in the day consistently helps now, and perhaps ST at the same time will assist as he'll be more tired and settle more quickly than if he is UT.
If you like we could look at your EASY for a few days (if you want to post) and come up with a plan for you ST together and then we can also be here while you start, when you're ready. What do you think?
I hope that helps,
N x