Ask HN: which features shall we charge for?

We launched the free version of our website a few days ago at http://twendly.com/. We found that, as we've expected, people are using twendly to do researches. The Pages/Visit is 7.78; Avg. Time on Site is 00:07:15. Here is one message from one user: @wikiReader: @alexdong twendly.com is really cool :) -- just spent a good 20 min with interesting results.

Now we have a few features we could charge for:

#1. More search results: eg, you're preparing for ycombinator interview, you want to get a sense of what does it feel like, so you search for http://twendly.com/?q=ycombinator+interview. Right now we're displaying only 10 people in the result set, we could charge people to see, say, 100 results. (This is one of Linkedin's business model. )

#2. Deep drill-down: eg, you want to check out Dustin's tweets about memcached http://bit.ly/5uV6hW, we only show matches within last 12 months. Potentially we could show all of them or even allow user to click on the monthly breakdown to filter by month. Deep index is one of our advantages.

#3. Automated Twitter list: eg, if you want to follow people who talks about couchdb, you'll have to click each follow link and maintain the twitter list by yourself. We've already got the code to make a search into a 'dynamic list' sync with search results.

#4. Adsense type news. Allow people pay to put their ads onto the search results.

What do you think? Reasonable to charge for these? How much shall we charge for? Why?

Cheers, Alex