1. Do you think Google looks at this on a domain level? Or do you think this needs to be done with every page on the site?
Google definitely looks at both URLs and domain as a whole, but more importantly they look at the individual links. You can't simply dilute out bad links except in extreme cases (ie: big brands). Penguin is a machine learning program - it looks at far more signals than just percentages. A combination of enough of these signals can result in lost rankings.
2. What would be a good way to build links fast to the pages, need to build lots of links to be able to dilute the profile. I was considering Dripable, or a similar service, but decided i really don't want to create more spam.What would you do?
You will probably have trouble attracting natural links to the old pages, especially if they are just product or service listings. I would consider creating new pages that have very valuable, evergreen content. Promote those pages via social media, press releases, and more main-stream marketing that builds a healthy link profile. Then 301 redirect your current less-than-savory pages to these.
**3. What would you say the % threshold for anchor text is, i have read on different sources that at least 40% - 60% of links should be branded, url, or generic anchor links. Do you think this is accurate? **
If you really must insist on using a %, then that % should be based on the sites that are already ranking for those terms. Your best bet would be to choose the industry leader in your space and see what their link profile and percentages look like. In most cases, you will be surprised to see that they tend to have much lower thresholds than the others. Bear in mind, though, that your best bet is to probably scrub out bad links wherever as possible - they represent not just potential rankings losses, but a stain on your brand.
At a more general level, you should expect that the majority of your links to any "optimized" page should be greatly varied, brand and navigational heavy, and only use exact anchor text sparingly. Think of anchor text as merely an external validation of your relevance to that term. You don't need to sprinkle many in for Google to get the picture.
Hope that helps!