Since everything is round, shifting can occur. To prevent any shifting during glue up, I would glue in the dowel first (use very little epoxy, you can even stick the knife tang in making sure there is full contact between woods), and square your tang slot to the block. The part of your dowel that protrudes out, will couple with your ferrule, with spacer sandwiched in between. So you need to calculate how deep to drill into the block, and the ferrule, so you have a neat fit. And remember, if everything is fitted well, you will need very little epoxy for internal gluing.
Also, don't leave too much thickness on the face end of your ferrule, where you will shape your tang slot, maybe 1/4" at most.
You can shape the tang slot on your face end of the ferrule before assembly (I would), or after the handle has been glued together. Eather way, you will need to drill a pilot hole with a small bit after your drilled the dowel hole. If you shape before glue up, you can drill several side by side if you XY Drill Vis), and then shape the tang slot with files.
When you glue up, insert a flat piece of metal to align the slot on the ferrule and on the dowel.
As WillC pointed out in his post, it is good to let epoxy set a little bit before clamping, so you don't have much shifting. I assume you will shape the handle after it has been glued up.
Using dowel will reinforce a structure of a handle, allowing for metal spacers. Even if metal heats up, it won't affect the handle, as the dowel is what holds parts of the handle together.