As much as you can, there aren't any fixed number. But I guess 100k quality do-follow backlinks are enough.
Yeah, you do not want to build too many links to fast.. Your best bet is to spread it out over several months. Also 100k is extreme to get PR 1. As long has you have quality links, which means links with PR, you should be able to get that PR 1 assuming your site has fairly good quality.
There are no specific numbers of links you need to gain PR. I suggest you not to waste your time in dofollow links only. Though I'm not saying that you shouldn't get dofollow links. Just work naturally. If you have a chance to get juice from a particular link, do it as long as it hasn't been attacked by blatant spammers.
I think no body can answer of your question. Only Google knows the answer. Continue creating good quality backlinks, until the next update of PR.
at first i want to say that you have to follow some steps like : 1. On page optimization (correctly add different tags) 2. make your site content rich. try to think about the quality of your contents 1st. 3. then Go for link building. just a few links from popular high PR sites , directories, will boost up your position and continue this process i don't think you need a lot of links for getting PR1. thanks
http://www.kirfan.com/link-building-mistakes/ here is the tips of link buiilding and the things you should avoid doing it
You don't to be called a spammer right? so build your links naturally. If you added too many link at one time the drawback is yours! Negative Results for sure..
it's not about the quantity of dofollow link to your site, but it's about the quality dofollow link to your site.