Poster #27,
Why not start a new thread in this forum?
You will then get various opinions.
(Removed)
The lintel & the bricks that we can see are infill and can safely be removed but first hack off plaster above the centre of the lintel, go up a few courses & you should expose the original brick arch.
Only after exposing the brick arch can you remove the infill & lintel.
Leave the chimney breast outside corners intact - stay away from them.
How many fireplaces you have in the house? Then you have that many flues that might need sweeping.
Dont "wash" any of the flues or fireplace openings.
Definitely, It would be best to remove the fireback and the infill before sweeping.