Yes, this kind of 2 stroke engine is the very traditional style, don't think it is complicate Change a new glow plug after the break in.
Most definition of break in complete means the stage that the piston doesn't jam in the cyclinder anymore. You can turn the fly wheel before and after you will know. (some engine in completely cool down still have little jam but it is normal).
not necessary, just renew the glow plug to start the tunning. The "metal dust" during the break in process will follow the air flow to the exhaust but some of them will attach to the glow plug element and make the glow plug down performance or fail which will affect the tunning afterwards.