Baileys woodland pro is a cannon bar.
the ebay deal sounds good
Baileys lists a different kit for the MS250 but in the Oregon catalogue it is the same powermate part 544658X
The file should be a standard 5/32"
Be aware that the 250 is overspowered for the rating of the carving chain. (rated at 38cc)
The MS250 is also heavier than the MS170.
If you are comfortable with the heavier saw you may be happier with the extra power.
If you are a beginner on chainsaws and carving stay with the MS170.
Just my opinion