Linux and all the hosting services you need are already inside the box. Rack-mounted servers are significantly more attractive to ISPs than PCs. They're easier to service, run cooler, and take up less space. Some of your services need a big, honking server with multiple processors and a couple of hundred gigs of disk space, but some of your customers will run better when isolated on a smaller server. It's best to keep them away from other customers, and a small, dedicated machine is the right way to do it.
Rackable servers are the way to start small and grow, but with a plan.
I've seen too many ISPs who started out with conventional tower and desktop machines, and soon had an ungainly pile of machines, hubs, and routers. When you needed to get to something at the bottom, it was nearly impossible. From busy Webmaster to occasional user, CuteFTP has the features you need. I've been a CuteFTP user ever since it was a prerelease beta program. I've tried others, but never found a reason to switch.