If you need this done quickly and professionally, you need to put some of that $30k towards someone who knows what they're doing. While you can learn this stuff, the chances are you won't learn quick enough to avoid alienating a fair chunk of your customer base.
People will recommend EC2 and all sorts of other cloud setups, and they're an option too, but I'm old school and lean towards physical plant I can trust (and kick -- or at least visualise kicking -- if frustration overwhelms me). If you get someone in to help you (again, highly recommended) you'll almost certainly end up working with whatever they know best -- and there's nothing wrong with that. There's nothing inherently "wrong" with any solution, merely tradeoffs.
To the subject at hand: I wouldn't be inclined to buy servers outright. Renting them, whilst a longer-term large cost, is cheaper in the short term, which helps keep you cashflow positive. It's also easier to add a new one here and there, and it's (usually) the provider's problem to deal with spare parts and repairs (make sure of this, though). Eventually, it becomes more cost effective to do it yourself (your own hardware, racks, network, etc), but that time is a long way off.
As to specific hardware, you should get the biggest machine you can afford (within reason) for your database server. Those things are really hard to scale well, so throwing hardware at it is an excellent strategy. For webservers, utility servers, etc, dial back the shiny lust and target the price/performance "knee" (the most economical point on the price/performance curve) and make sure your application can horizontally scale across many servers to take advantage of that economy.
When talking to a provider, make sure they can quickly provision a replacement for any failed server, and check their SLA for restoration -- it's very rare that they'll cover you for anything like the actual cost of downtime, so don't forget to budget for redundancy and backups. There's no point building up your service only to have it disintegrate when your DB server goes down for two days and all your customers desert you.