I bought a Spear & Jackson trowel and hawk some 17 years ago and they have had a fair bit of use over the years. I don't think you can buy these anymore but general advice is....
My trowel (float) has been used for both base coat and finish, if possible try to use one for each. I found that bonding coat seems to be especially detrimental to the metal finish if not cleaned immediately after use.
As far as breaking in the trowel, you can buy ready broken in trowels but I wouldn't worry about this detail from a diyer point of view.
Main tip for diy plastering is use plenty of diluted pva to seal brickwork and old plaster first! Buy in bulk from Screwfix or similar to save loads of money to let you avoid skimping on using it!