WordPress just rocks, there's no other way to describe it.
With respect to your questions here are some answers:
- Easy to manipulate: WordPress has an extensible API that has allows 3rd party developers to write plugins for it. There's a wealth of plugins out there doing everything you can imagine. And if you can code in PHP you can write your own plugins for it too. I needed a plugin that sends an email to a commentor on my blog when I reply to their comment, so I just wrote one.
- Spam: For me, spam has become a thing of the past. WordPress comes with a magnificent plugin called Askimet which catches 99.9% of the spam that hits my website. If that's not good enough for you, you can also implement another plugin called Bad Behaviour which makes it practically impossible for automated spam to get through. That's unless you want to implement any captcha or another other anti-spam plugins that exists out there.
- Customising layouts: There's a wealth of themes for WordPress out there and I mean literally thousands of them. Creating your own is also very easy if you know a bit of CSS/HTML. It's always much easier though to find one similar to what you want and customise it.
If you still don't feel confident about it, one option would be to set up a temporary blog in a separate folder on your website and just use it to familiarise yourself with the product and it's capabilities. If you need any help/instructions, just ask on this forum.