Contact the owner. Before so much as hinting at a price, simply email to ask whether or not the domain is for sale. If you are known or can clearly be linked to a thriving business, create a generic alternate email address through which to contact them, as your success might be leveraged against you. Be aware, however, that an informal-sounding email address is more likely to be regarded as spam or junk mail.
In terms of what many vendors call unlimited service, Web Hosting Pad's terms of service indicate that its definition of unlimited is what it calls "incremental." Basically, as you need more capability, it wants to discuss that with you, both to help you get the most out of its services, and to make sure you're using its systems without abusing them.
When it comes to server operating systems, Linux is typically the default option. Still, some services offer a choice of Linux or Windows hosting. If you have specific server-side applications that require Windows, such as SQL Server or a custom application written in .NET, then you need to make sure your web host has Windows hosting. But don't let the idea of a Linux host intimidate you. Nowadays, most web hosts offer a graphical interface or a control panel to simplify server administration and website management. Instead of typing at the command line, you'll click easily identifiable icons.
It shouldn't come as any surprise that, like other web host providers, A2 Hosting's unlimited plans aren't actually unlimited. It expect you to use its service like "similarly situated customers." This is like being on a highway. If everyone is going a few miles above the speed limit, you're probably okay, but if you're barreling down the fast lane past everyone else, you're probably going to be asked to slow down.
Complete Internet Solutions is not like that. The price they quote is your locked-in price. In addition, they offer a free twelve months on top of your term. So, if you sign up for two years at $3.95 a month, you pay $94.80 for the two years, and then pay nothing for another year. If you choose to renew at the end of those three years, you can repeat that pricing program without a fee increase. This is how it should be done.
Think of your domain name as a street address for your website. Without a domain name, you would have to tell customers to visit your website at an IP-based url such as 184.108.40.206/~yourwebsite instead of yourwebsite.com. The former is not very memorable or friendly to human eyes and will surely result in not that many visits to your website. While it is not mandatory that you have a website domain name, nor is it mandatory that a domain you own be attached to a website, for a successful online presence you truly will want to get your own domain name to ensure your website has the proper air of professionalism and appropriate branding.