I was wondering about a sitemap for my webshop. Is it necessary to submit one to Google or other search engines? Would it help with getting indexed properly, and if so, what pages should I include or exclude?

I already have a simple sitemap for my normal website (illustration portfolio) but if I generate a new XML sitemap (for my webshop), it gets stuffed with all kinds of urls.

Thanks.

I did remove all unnecessary urls and items, now I have a clean xml file

I always include all URLs in my sitemaps that my website's system generates and I leave it up to search engine to decide whether it will include them in it's index or not. But be sure to set proper "priority" and "changefreq" in your sitemaps.

<changefreq>weekly</changefreq>
<priority>0.9</priority>

Such as set high "priority" (eg.: 1.0) for those pages of your website that are important for you, such large image preview pages, and set low "priority" (eg.: 0.1) for just some miscellaneous search results, etc.