500 MB is actually quite a lot. You should be able to run most things on it.
Looking at your site (those are some adorable photos!), the first thing that jumps out at me is that you are using photos, which are large, and can slow your site down. But I don't think they're your issue here.
The problem I think you're having is in part from your plugins. This is probably totally obvious to you, but the more times your website calls out to external servers, the slower it gets. Logical, right?
When I looked at the source code of your main site, I saw multiple instances of jquery, coming from external sources.
The worst part is that jquery comes with WordPress! So no plugin or theme should be calling out to an external site. I would contact the makers of 'sunshine-pro' and tell them to use wp_enequeue_script() instead of calling an external jquery, as it will help a LOT of people.
If I had to pick a plugin on your site that would be suspect, it would be flexsitez. I went to your server and looked a little at that code, and right away they're doing a number of things 'wrong' (such as calling wp-config.php from the plugin file directly). The weirdest thing is that I'm actually pretty sure that flexsitez is a theme, not a plugin, so it's in the wrong place and possible causing some of your issues.
I would also recommend you remove some of your plugins since you've got some duplicated effort going on there.
Jetpack has a sharing module, which would replace the need for simple-twitter-link and possibly facebook, depending on how you're using it. It also has WP.com Statts, which obviates the need for official-statcounter-plugin-for-wordpress.
While I know that's a lot to start banging on, one cheap and easy way to speed up your site would be to start using caching. You're already using pagespeed (yay!), so WP-Super-Cache would be a pretty simple way to make your site faster for users. I also wrrote a little explanation on how you can customize pagespeed on your site by editing your .htaccess file: http://elftest.net/kick-pagespeed-up-a-notch/
I hope that helps you out some!