Thank you for the comment and questions.
1. Linking to the guest poster’s website. That depends on the site. Is it a trusted resource, does it add value or is it there just for SEO. If it is just for SEO, no follow.
2. If you’re guest posting for backlinks, ask yourself the same thing. Is it obvious that you are doing this for SEO, if so, no follow. If it is natural and you’re adding value in the guest post, you may want to go for the do follow link. But make sure the site is high quality and won’t cause damage.
3. Link to pages that add value to your visitors. If it is a product page and you are not monetizing it, you can do follow, especially if it is relevant, authoritative and provides value.
Everything in SEO at this point is case by case. With that said, as a rule of thumb, if you’re monetizing, no follow. If it is helpful, useful, not monetized and will be around for a long time, you may want to give a do follow link.
I hope this helps,