How should I structure finances for experiments? I'd like these activities to be separate from my personal assets.

Reading Lean Startup makes me keen to test the waters and try out some ideas to see if they might eventually become a business.

This might involve projects in very different areas with different names and functions.

During this stage, before any of these ideas would be established enough to form a company around, how should I deal with any income generated.

I am in the UK, where it is fine to operate as a sole trader, however you do not have any liability protection, should someone feel you've stolen their idea or have a complaint against you.

Is it possible to set up a limited company to receive all revenue (no matter how small!) from all these various activities - even though there will be various sites/services/products?

When you register a company, there's no rule on how many products or services you can sell through it.

My only concern would be if you have projects of significantly different risks. For example, if you have an affiliate sales site, that's probably low risk and not very open to lawsuits. Alternatively, an AirBnB clone would be much higher risk.. a poor ToS/ToU combined with a malicious user would be a terrible combination.

In that sort of scenario, you may want to isolate the products/services in some way. That may be as simple as different legal entities, but I honestly don't know that part.

And for the record, as long as you don't have any wrongdoing, getting sued is a sign of success. It means you've been successful enough that someone else has noticed that you are challenging them.