Planning is the key to everything.
Decide on your aims, research your potential custoimers, their buying habits, how they use the internet, their disposalbe income and so on. Think about your marketing plan, budget, finacial projections and escape plan.
It's only when you have a viable busienss plan that you need to consider the scope of the website. You will discover that most products have their limitations, one CMS will have 90% of the features you want but another will have the reamining 10% but fail in some crtical area. you could go bespoke but that may tie you to a specific developer and hosting package.
You may consider running a test site with PPC to determine if the idea is viable. You might just go with a very simple site, just an offer and means to get the product.
It's the business plan that will indicate the type of site your need. RSS, twitter, blogging, affilites are just the icing on the cake, almost addons you can play with once the main site is up and running. Remember as well that internet usage is constantly changing, squidoo was the answwer to everything a while back, now it's local search that seems to be popular, tomorrow it may be mobile computing that gets the thumbs up. You need to have a flexible approach to your website, be realdt to constantly experiment and test to see what works and what doesn't. Twitter might be a a good marketing tool for you but it should be part of your plan not the core. Same with RSS or article writing, they are just tools you use as part of you marketing strategy ready to be discarded when they fall from grace.