Help me come up with idea please

I would suggest to play a legacy challenge where you will randomise everything about the sims life. From their traits, aspirations, careers, favourite colours(where you need to be creative in CAS or their house interiors), lot traits, lot size, neighbourhood, to name a few. There's no points to be calculated but the thrill that you're going to have while playing with your Sims. For example, I have a Sim with a loner trait but her aspiration is to be Friends of the World, she's also an Oracle, and gave birth to a vampire (she's the spouse of my 3rd generation family). It's pretty intense but, she's surviving. It will let you play with different & unique Sims since you're giving them a character that is out of your comfort zone. I also come to realise that, it is much easier to let the Sims to live in a simple house rather than huge mansion. As of now, for this particular family, they live in a huge estate as the family has been prosperous for the past 3 generations, but now, they are trying to make as much as they can by selling paintings as well as from the salary that they earned, just for to the pay bills & their employees (butlers, maid, gardener). I guess, it's true that old money will never last that long.

Try to play with the occults & the lot traits too. For my case for example, my founder house has on a dark lei line (from the randomise result). She gave birth to a twin (1 is a normal Sims while the other is a vampire). I never have any intention to have a vampire to start of a family, but this twist come so well, and I pretty much enjoying it. Just that, I randomly change their lot traits whenever the next heir took over the house & starts their own family. As of now, I'm on my 4th generations with 6 households from the same founder. For the ownership of the houses, I always give it to the male Sims (he can be the eldest or the youngest) because the female Sims are going to get married to the other Sims where they're going to start their own families.

I also let my Sims to own businesses such as retails/vets/restaurant if they have spare cash to spend besides going for vacations.

I would say that, this is a pretty easy & fun way to play with your Sims, given what the games have at the moment. There's no set of rules except that you just need to randomise everything and let the system work it out for you & having fun playing along with them. If you're getting bored playing with the Sims, try to renovate the community lots so that your Sims could have a fun time the next time you're going to play them.