Ask HN: Should I be using double opt-in for my web app?

I have a web app that is a resource and tutorial database for web developers/designers: http://pineapple.io . There are a few different things I would like to do, and I'm a bit confused as to the best way to proceed.

My goals:

1. Send a welcome email

2. Send an email out to my users if I add a major feature

Secondary goals:

1. I want to include a feature where if they so desire, they can get a 'digest' of the best resources of the week. I guess this should be separate as most people might not want that? Or they may, I am not sure. I think it would definitely help with user retention rate so if people don't want to visit my site they can still stay in the loop.

My questions

1. I really don't want double opt-in. I find this more annoying when sites do this, because it's an extra email. If I want to unsubscribe I'll do it directly from the first unwanted email. Is this a 'required' thing? Everyone says its quite important, yet I'm pretty sure huge websites like twitter don't do it? Mailchimp and aweber advocate it heavily.

2. What might be the best way to handle my secondary goal? Would it be best to take the twitter approach and instantly sign them up to this digest, and let them unsubscribe easily (twitter has user digests, recent 'trending' tweets, etc. A few variations that you unsub from separately). Or, should I make it some kind of secondary feature on my site, maybe in the sidebar?

My ideal scenario: A user signs up to my site and is automatically subscribed to 2 lists. They receive 1 welcome email. The lists they are subbed to are my 'website updates' list (rare.. once a month if that), and my 'weekly digest' list. They can unsub from the weekly resources list on the first one they receive. At some point they may get a website update email, and if they dont want those either they can unsub from that.

I dont want to be irritating to any users though so let me know what you think of this setup.

Thanks