page redirect question

[Cove]

I am learning this whole SEO thing now few questions on page redirects.

To explain I went into my webmaster tools and noticed a few thousand pages not being crawled because of errors and noticed they are pages I deleted a long time ago.

BASed on that

1. Does this affect you whole site SERPs if you have crawl errors?

2. How do I enter pages I want google to stop looking for?

3. I want to delete products and create them again with a better product ID. Will page redirect work if I delete products and create them with the new ID pointing the old id to this new id?

[Swirleigh]

I try to clean up all errors in my webmaster tools, especially 404s. I believe you can loose trust value.

Questions:
Is your sitemap still linking to these old pages?
Are any of your pages still linking to any of these now non-existent pages? If so, Google would follow the links to find the pages.

Run your site through xenu or screaming frog to find bad links in your site.

Redirects, using 301s would work.