...Also a good idea would be to only activate bonuses when you know you'll be able to get more than 12 free rolls.
That's the most important advice regarding bonuses. You should make at 12 free rolls to break even with the reward points you've spent to activate the bonus. I recommend you activate a bonus only in days you can make at least 14-15 free rolls, which will ensure you will have some profit. Otherwise spending reward points on a bonus is not worth it.
The other thing is that it's best to activate both a FREE BTC bonus and a Reward Points Bonus. Thus you will easily recover some of the rewards points spent for activating the bonus while earning more bitcoins per free roll.