few questions about LCIS

Hello! I'm Malena, (44 years old, perimenopausal,"third-degree relative with a history of canceR) and I’ve been diagnosed with LCIS. I have a few questions:

How effective is treatment with tamoxifen 5 mg for LCIS?
In my country, 5 mg tablets are not available. Do doctors recommend splitting a 10 mg tablet, or taking 10 mg every other day instead?
How effective is omega-3 supplementation in preventing breast cancer?
Is it recommended to undergo genomic testing? (I don’t have children, only a niece.
Best regards....