Buying your domain name seems pretty simple on the surface, but there a few things you should keep in mind when shopping. While there are no limits to the number of domain names you can purchase and forward to your hosted website, you should have a primary domain name that you tie your analytics and marketing.
There are many domain extensions (.com, .net, .hosting) to pick from, if possible the .com is usually something you'll want to own. With the many new extensions available or waiting to be released, you can pick up some unique options, such as www.karmicvisions.graphics. Here's a good link for a listing of the different top level domains.
Should you buy all the variations? That will probably come down to your budget since each domain has a cost and you have to renew it annually, unless you purchase for multiple years, so you'll have to decide on what you'd want to budget toward this level of ownership.
The other thing you'll need to keep in mind and perhaps consult your attorney about, is trademark/copyright issues. Although anyone can go to a domain registrar and purchase anything that is available, that doesn't mean it's truly safe to do so.
There are many domain registrars available, price being the main differences. Usually it's a good ideal to use a registrar that is easy to move from in case you don't care for their service or pricing. Please keep in mind you can not move your domain name to a different registrar within 60 days from the purchase date. We're currently using NameSilo and are very pleased with the service and pricing.