I have cut both the bladed scarf joint and the stop splayed tabled scarf with under squinted butts and wedges.

But it depends on whether or not your two timbers you are joining will be in tension or not.

Some scarfs are not the best for tension timbers, because the stress is put into the pegs or fasteners holding the two pieces together.

Your scarf will depend on where they are in your frame and whether or not your timbers are in tension.
Your question says that these are plates, these usually aren't in tension like a tie beam is, so you maybe able to use a fairly simply scarf joint.

There is a free download from the guild, the Historic joinery series has one chapter on scarfs. Chapter 6.
You should download that and read it.

And to answer your question about the brace joint coming in to the scarf joint location, your brace should support the scarf joint location.



Normally I like to have the lower side of the scarf being supported by the brace.

If you want you can call me and we can talk about your scarf joints and locations.
Jim Rogers