Yes. Casinos often provide the option to download some slot machines for offline play. You can play them without access to the Internet.
No. The return percentage, volatility, number of reels, coefficients, and other parameters are the same in the demo and paid versions.
Yes. Gambling websites work on smartphones. You can run them from your browser or a downloadable app.
You can see them on the page with the slot machine.
When you refresh the page, the virtual coins will be credited to your balance again. You can play free casino games as much as you like.