Germanic lineage arrived from the east?

[Jaska]

1. Indo-European 'stone' > Slavic with consonant metathesis --> Germanic 'stone, hammer' --> Finnic *hamara

Slavic consonant metathesis is quite young phenomenon. Likely late 1 M AD.
From wiki
"The liquid metathesis occurred in the Common Slavic era. It took place after or was still productive until the end of the 8th century. The name of Charlemagne, who died in 814, underwent the change:

Old High German Karl[note 1] > PSl. *karl′u[note 2] > Common Slavic *korl′ь > Russian koról′, Polish król, Slovak kráľ, Serbo-Croatian krȃlj
On the other hand, the change had already been completed in the earliest Old Church Slavonic documents. That implies that the change was completed, at least in the dialects of Bulgaria and of Macedonia, in no later than the 9th century, when the documents were written. There are, however, some attested unmetathised words in OCS such as ал(ъ)дии, a doublet of the metathised ладии."

That is a well-known post-Proto-Slavic phenomenon, and it can be recognized because it only concerns part of the Slavic languages. But I did not speak about that. The metathesis seen in the word 'stone' (*akm- > *kam-) is much earlier (all Slavic languages participated in it) and purely irregular development without any further examples.