many adsense sites

you are fine if they are not spam or MFA, otherwise your account will be banned and all sites will be deindexed.

search this forum, you will find many examples.

If you are following the policy then no problem. But my advise is try not putting all eggs in one basket. =D

Google doesn't care about how many sites you monetize with AdSense.

It is the quality of the sites that can get you into trouble.

So if you build your sites with good content, you have nothing to worry about.

As stated, as long as you try to actually keep them high-quality and user-oriented, you should be fine (provided you don't violate TOS).

Google will not have a problem as long as these sites add value to the end-user, but:

I often hear of people who run over fifty sites and they earn X amount from those sites. When they reveal how much they are earning I am usually startled because what they earn from their large portfolio I am able to earn the same from one site.

My advice will be to build a smaller amount of bigger sites that target various keywords. You can create multiple categories on one site that are related and rank each page/category as though it were a seperate site.

For instance: you can create a site about acne and have multiple categories targeting "facial acne", "back acne", "teenage acne", "acne in adults" etc.

Following a model like this is more sustainable over the long-term and instead of the added costs of paying for multiple domains you just pay for a handful of domains. You will also find that you will be able optimize each site much better because your focus will not be scattered and after a while the site will begin to rank naturally for new pages that are added because of the internal juice that flows.