I am a newbie and I want to start a website for generating revenue from adsense.

I've registered a domain and will use this domain for multiple niches and topics.

I would like to optimized my homepage as well as the niches site. But I am not sure which method/system has advantage when comes to SEO.

My questions are:-

Folder vs. Subdomain
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a)Should I use folder or subdomain for the each niche/topic?

b)What is the rule of tumb when comes to subdomain and folder usage? Which one to choose under which cricumstances?

Homepage : Blog vs. Directory
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At first, I am thinking of using blog as my homepage where I post some related articles to each niche with links to the niche site(subdomain/folder). But then I think I can do so by creating a folder for the blog itself.

I've also heard that directory/portal is also in favored by the search engine. So now I am thinking of using directory/portal for my homepage.

a)Is it true directory/portal is good for SEO?

b)What is the best for homepage(when comes to SEO), blog or portal/directory?

Seeking you guys expert advice.

Thanks.