357 ammo of any kind won’t chamber in a 350 Legend. Hand loading .357 or .358 bullets in a 350 legend would be real bad.
Yours apparently has different chamber dimensions than mine. Rounds loaded with .357" or .358" bullets will fit the chamber with a couple thousandths to spare; the issue is the small throat diameter.
Loading and firing .357" bullets in a .355" bore is not a big deal; just start low and work up. Max loads are a little below the same for .355" bullets, but less difference than some would expect.
On the 5.56 brass question - you can expand the necks out to 35 cal as has been done long before the Legend, and when fired in the 350 Legend they expand to fit the chamber just in front of the case web, looking about the same as fired brass from some of the looser hunting rifle chambers I've used. However, after trimming the brass to square up the case necks, the brass ends up about .050" too short for the Legend chamber - no go, can't use it that way.
