Hi Juan, and thanks for you best wishes.
Pricing is something you need to research on the selling platform you will be using, for example ebay.com.au
It would be no good listing products $10.00 dearer than your competitors, so you need to see what your products, or products very similar are being priced at.
Regarding the best stock to sell, again that question can really only be answered by research. You can try one of each and measure your response, but don't just measure it over a week.
To accurate data you have to allow for market movements, so you could well need to research things like that over quite a few months, and that will of course be costing you in listing fees.
The one big thing you do want to watch out for is your listing fees, just keep in mind that the dearer the product, the more you will be paying to list, so the more profit margin you will need to make to cover yourself.
First things first, research your selling platform to gauge other product prices, that will tell you where your pricing model should be set.
Just PM me if I can be of any further help.