Unless your site is going to receive a ton of visitors, pretty much any reasonably contemporary processor will have enough juice to quickly supply pages from that cache. As you put more static pages on the site, at worst you simply have to add enough RAM to let the system fulfill 90 percent or more of the page requests from its cache. Move to any type of dynamic content, however, and you're stepping into a dramatically more complex world. If you do a little homework before you take this step, you can save a lot of time, money, and heartache. The first place you'll feel the effects of this complexity is the server's hardware setup.
Dynamic content places an enormously larger load on a server's processor than static pages.
If the workload involves database retrievals, the load on the processor greatly increases yet again. The most obvious and direct way to deal with the heavier workload is to throw processing power at it. If the server can handle multiple processors, you can add one or more additional CPUs. With the extra processing power, the server will be able to better handle the load of creating pages dynamically. If the amount of dynamic content you're planning to add is small, or if your current server has a lot of processor headroom, this obvious approach is probably fine.