Could you describe what this stellar node/lumens/blockchain is all about? Is it another form of cryptocurrency? Maybe build something like that for bitcoin, as you will find a bigger audience who would be interested in doing the tasks. I'd stay away from anything that sells incentivized "clicks" because real quality advertisers won't be long term customers, but registration and other small tasks would be a good idea.
Stellar is faster than bitcoin and the network fee is much more affordable (100k transactions for 1 lumen), so bitcoin is not an option in a project like that (where average transactions are less than 100 usd). If you like to know more, coinbase has a bunch of short videos about stellar.
Please further more the details?like what the post above says it seems that it is not completely explained so we can't give a exact answer.
There are a lot of projects like that, you can google if you like to know more, even amazon has a project like that.
2. As long as it is a legit task and doesn't include any illegal activity or downloading of suspicious apps or visiting of suspicious links.
Unfortunately, there will always be something like that. Finding a balance between preventing fraud or illegal activities and not annoy innocent uses is extremely hard.