When you click on the Clock in the top-right of the screen. Then "Speed by Reset", then "Increase speed of cash, hearts & skills by..." that number. You should reset that when it is as high as you can get it without waiting about 4 hours. You will be essentially restarting the game. Your Skills and Cash will increase faster. When you can complete Indra that number will be about 100. This is what Hornypony means by you can get about 3000 per month by actively playing.
basically, yes. Every time it makes sense.
yes, then next time around it will be 4 days, then 2 days, then 1 day; eventually you have skill level 30 in a matter of seconds. Spend your diamonds on Warp-Bonus.