Hi Steve, and welcome back!
You have had an especially tough winter, I’ve heard. This is all repairable (except for the door handles, see below).
From your first photo, it looks like the DuraTech cap may be loose as well. If that’s the case, you’ll want to lift it off, then break up what’s left of your concrete crown if you installed one. (The crown is a layer of concrete on top of the brick. It is sloped downward to the edges so water runs off the edges rather than seeps down into the mortar joints.)
Remove loose bricks, brush to clean up the surfaces, then mix up refractory mortar (NOT plain old Type S mortar) and re-lay the brick. Use more refractory to make a chimney crown, then use the same kind of silicone sealant that originally came with your DuraTech cap to set it back in place.
The cracks are easily repaired with a latex stucco patch and a putty knife. Wet them with your masonry sponge (not sopping, just a good damp) and then use the knife to smooth the stucco product into all the cracks, then feather it out. The patch has texture in it that will come close to matching your stucco.
As for the interior, I’d be very careful about doing what you suggest. Picking at one piece of mortar can inadvertently lead to pulling out a chunk, or starting a slow-motion avalanche over multiple fires that ends with mortar in your food.
The door handles need to be replaced if they burned so badly that they fell off. The replacement kit is exactly the same as the one that came with your doors, and it includes hardware. I know that BrickWood has got a new design in its early stages that will ship sometime before the end of the year, but it looks like you really love cooking in your oven and you’ve lost the use of your door until you fix it.
PREVENTION
I’ve talked about a chimney crown above. That really belongs here as well, because the lack of one combined with high heat and freeze-thaw cycles is what led to the mortar joints failing.
Here’s a couple of other things you should do to avoid a repeat of these issues:
- Paint the outside of your oven. It looks like bare stucco from the photo, and that will not stand up to the elements at all. You need a good outdoor deck or patio paint, applied annually. I use a roller and brush, and make sure to get in at the joints top (around chimney) and bottom (around base).
- Waterproof your chimney and exposed brick. Use a masonry sealant that’s food safe.
- Rule of thumb for your door: it’s meant to retain heat for baking, and should never be used for building a hot pizza-grade fire.
It’s clear from the photos that you really love your oven and are getting a lot of use out of it! Give it a little maintenance love and you’ll continue to enjoy it for many years to come.
Good luck and feel free to ask further questions.