Well. as for the reward/vip system:
Give you vip-level in % bonus for the first 3 deposits each month.
Make a fountain of freespins, where you once a month can get a random number of freespins (say 1-10) times your vip level.
Top loss prices: the people with the biggest losses have the best chance of winning 100 euro on each vip level (1-10, 11-20 and so on).
Weekly random spree: 100 cash prizes from 1-20 euro.
Other thoughts:
Build your own slot 10 freespins/draws:
either for communities or one self
have a variety of options, like how many reels, symbols theme, multiplying symbols, various bonus options.
Put 5-10 picks together and make the slot: spin 10 freespins or make 10 draws
Alternatively just make the slot and you can play it 100 times in your own currency.
Greets
M80DK