What do I research?

Now that I've picked a small niche, I've been doing a lot of research. So much that it might be a little overwhelming. I'm starting to jump ahead into what do I want my site to look like so that I know what kind of information to gather. Do I want my site to list all the types of products and link them to the merchant once they've decided on which type? Or do I want to rate all the sites and then lead them to the site? The former feels like it would have a higher conversion rate. The latter seems easier to do (which would be good to test this niche). So again I'm going to resort back to a spreadsheet to help me organize the information I need to find and what I find.

Product
What are the different types of this product?
Which products have better reviews?
Which products are most popular?
Which product are on every merchants' list?

Merchants
Who are the merchants?
Which merchants sell which type of product?
Which merchant has better prices?
Which merchant has better reviews?
What do I like about this particular merchant?
What do I not like about this particular merchant?
How does this merchant address the needs of the customer?
Who is their target customer?

I'm starting to wonder if this smaller niche is still too big..maybe I should do a microniche? I'll decided after I fill this spreadsheet.