Hi hon, it sounds to me like you've got a good action plan. Here are my thoughts...
1. 4-hour EASY (since naps are not going well this mostly applies to eating, but I think it's necessary to reset his clock)
Some EBF babies are not able to make a full 4hr EASY until they begin solids. But, you don't want to be feeding every 2hr either, because that does tend to cause snacking. What has worked well for some moms on here in this case is to do the main feed, then do a top up feed 1hr later (where you will eventually put solids into the routine) and then finish A time, nap, and do another main feed about 4hr later. I'd try this first before pushing straight to a 4hr EASY, because you don't want to worry about him waking up from naps hungry.
2. Not tanking up in the late afternoon, but giving a dreamfeed between 10-11
You'll have to see how he does with this. Some LOs this age do well with a DF, some don't. Some still like a natural cluster feed (feeding after the CN and then again before bed) and do well with it. I don't know that either one is necessarily right, so do what works best for him.
3. I will sleep in another room for the next few nights. We currently all sleep in the same room, and I wake as soon as LO stirs. My husband sleeps more soundly, so hopefully this will give LO a little more time to settle himself before I'm rushing to pick him up.
Really good. He needs a chance to settle himself in the MOTN!
4. Modify the shush-pat. Instead of shushing, we are using whistling and light placement of a hand on chest together with some PU/PD when necessary.
Modifying is a great plan. Some LOs are just bothered by either the shh, the pat, or both. I would be a bit careful about whistling though. I'm not sure what kind of whistling you mean, but I think it could stimulate him more than help him calm. You might just want to say your sleepy phrase in a soothing voice and keep your hand on him. But again, do what works for him!
5. Increasing awake time during the day. When we're able to get a better grip on naps, we will increase his awake to (I suspect to somewhere around 2.5h).
Yes, I agree his A time needs to increase. I think you're getting some UT naps and possibly getting stuck in an UT/OT cycle. I wouldn't wait until things start coming together though, I'd start right now. If you leave his A time too low, you'll never get out of the cycle. So, push it gently and gradually (maybe 5-10/15 min every few days) until he starts taking some better naps for you. Day sleep affects night sleep and vice versa!
Hope that helps! Let us know how it goes.