Multiple product specific niche sites, or one inclusive site with multiple products?

Hi Warriors,
This is my first thread on this amazing forum! I'm so glad I came across this invaluable resource. I just purchased Kenster's helpful Rags 2 Riches guide and I'm ready to put some of my ideas into action.

I've got a question for you experienced Warriors that has been causing me some grief and preventing me from getting started with my newest project. I hope it's not something that has already been discussed ad nauseum -- I really searched the forum first to see if I could find any opinions or advice on this topic before posting.

The Scenario:
I have a few affiliate products that I plan on promoting. Let's say, for example, that I've found a well paying product on how to master the game of Chess, and another product that teaches you tricks to be a Checkers wizard.

The Question:
Would you recommend creating several stand alone sites that focus one just 1 niche, with separate domains for each of these products, i.e.

"chessmaster.com" and
"checkerswizard.com",

or might I get better results with one site that could be used to promote both products (or future products) and has a more general theme, such as

"boardgamesmaster.com"?

My Thoughts:
Obviously, creating a bunch of little sites could be a bit more trouble to maintain, as well as the added expense of additional domains (which I realize is pretty nominal, but still should be considered). However, is there an SEO benefit to having two sites, that are unique but similar in theme that could link to each other (especially if they are created on different servers?)

Your advice may be a bit different if you take into consideration that I don't plan on paying for traffic for these sites (or site) early on, but I intend to work hard writing helpful and good quality articles for the site so that it has real value and builds trust in my readers and helps drive organic traffic to the site. I don't intend the site to be a sales or squeeze page, but rather, a blog style site with helpful information, that also happens to promote a guide that I think will be even more helpful.

What if, a while down the road, I now want to add another boardgame product -- for Backgammon, say. I'm thinking that if I went the 1 site route, I may by this time already have a site with a fair amount of traffic, and now when I add a new category for the new 'board game' related product, I've already got built in readers and customers. If I did the multiple site route, I would have to create a brand new 'backgammonwizard.com' site that would have no initial traffic or credibility. I'd be starting from scratch, right?

Because of these ideas, I'm currently leaning towards the more broad, single site, multiple niche set up.

However, from what I've read in this forum (and many other places), it's really great from an SEO standpoint to have your keywords in your domain name, and for that reason, I'm thinking if someone was searching specifically for 'chess' they might find and visit the 'chessmaster' site before they went to the 'boardgamesmaster' site. Is this really a big deal?

Your Advice?
Does my plan for the site change anything? What do you have to say? Do any of you have metrics on any of this or should I just try both methods myself and see which seems to work better?

Thank you for your input. Sorry about the novel. I tend to overthink things -- you never would have guessed, right?

I'm trying to follow everyone's 'Just take action' advice.

Will O.