Hi Luigi,
I favour cooperation with OpenCorporates instead of independently adding lots of company record to Wikidata. Sure there are parallel strategies but any effort should also include OpenCorporates to some degree.
OpenCorporates is licensed under ODbL (just added this referenced statement to Q7095760) and we have property P1320 to link Wikidata and OpenCorporates. A first step would be to align
https://opencorporates.com/registers https://en.wikipedia.org/wiki/List_of_company_registers
Right now we have 18 instances of company register (Q1394657) and its subclasses explicitly classified as such in Wikidata.
These items should be linked with the registers listed at OpenCorporates, e.g.
UK Companies House (Q257303) = https://opencorporates.com/registers/270
I've also noticed that OpenCorporates has a field for "Identifiers" where Wikidata QIDs may be included to have two-way-links between the two datasets.
Anyway, better contact https://opencorporates.com/info/contributing at least to let them know about your plans.
Cheers, Jakob