I have Text-Link-Ads AND AdSense on the same pages. It is perfectly allowed to have both. TLA make an extra 21 USD for me a month on one site, which is not a lot but guaranteed income, which is more than I can say for AdSense, some days less some days more. i just wish I could sell more of the links on the site, only three sold so far.
You can use any program that is not contextual pretty much. A Contextual Program's simple definition: One that reads the web page it is on and shows relevant ads depending on the content. (So your answer would be - yes)
yes, you can use adsense or any other cpc ads. And they pay every month, I get it through paypal. It is like fixed income unlike cpc. Depends on how many people buy links.
Well, currently I am trying with sta-ads. But I am not really sure whether they r scam or not. But I will find it soon.