Seems like a reasonable solution to this problem. Heli-coil inserts are strong and should last pretty much forever if properly installed. Not knowing your location, I would suggest that you find a machine shop that does auto engine work. They have probably used heli-coils before and may have everything needed except the actual insert.
This really isn't a bicycle-specific repair, even though it is a crank arm. it's more of a machine shop 10-15 minute job.
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Dale, NL4T