In a typical business model, the cost of buying one or two extra domain names is minimal. You don’t need any hosting with them, just the registration. If you think they might be useful, far better to get them know before they get stolen by cybersquatters
.net might be a relevant second choice, but it depends on your target audience - both in location and in nature - as to what other TLDs people are used to trying. Here in the UK, for a general non-technical audience, it would be a poor choice because it isn’t one that people commonly use.
It really depends on the project and name you’re buying. Many people spend thousands getting their brand trademarked in order to protect the assets of their name and how it’s associated. In comparison, buying up a bunch of TLD’s (which would probably end up at a lesser amount than $200) would give you a basic level of protection over your brand and give you some defence against the cyber-squatters. Sometimes a bit of preventative measures can be a good thing, especially if it avoids the stress of pursuing someone legally. As for myself, I bought COM / NET / ORG / BIZ / INFO and the regional TLD’s (UK and EU) for my brand.
It depends on what your website is all about, if it’s a website based on general infomation then yes go for the .com extension. But if your website is based on information for your country, e.g. - a plumber, then I’d go for your countries extension first, the .com can come later.