It depends if you're giving it to a client and if there's going to be much in the way of CMS functionality.
Looking at that template, I really can't see any need for as many as 10 addons. The only addon I'd say was worthwhile is Freeform, which handles form submissions nicely.
If giving it to a client, the ones I use most often are:
- [CE Image] for image manipulation.
- [SEO Lite] which just adds a meta title/description/keywords field (though this is not necessary and could be done through regular fields and a little logic).
- [Structure] which gives a nice UI to your pages which makes it much easier for a client to use and also helps with generating menus, sitemaps etc. (although again, this could be achieved with the standard EE [Pages][5] module but Structure is far easier for clients to understand in my opinion).
- [WYGWAM] which is just a rich text editor (again, not necessary as the standard EE one would be fine but WYGWAM is nicer to use).
These are mostly professionally maintained and updated regularly.
EE isn't really like something like Wordpress where you'd chuck in say, an image slider plugin. The best thing about EE is that it is so simple to pull data out of it that you'd just find a javascript slider and use EE to get the images out with something like:
<section class="header-gallery">
{header_images limit="4"}
<img src="{header_images:image}">
{/header_images}
</section>