Creating massive penalties equal to the whole cost of a house for anyone that sells after less than 6-8 years would have devastating unintended consequences. It might make flipping impractical, but it would also hurt a lot of people who find themselves in a position where they need to sell, and would increase the risks associated with buying a house for lower income buyers.

It would help if you targeted the profit from the sale instead of the whole price. Flipping is about buying low, minimizing the cost of improvements, and then selling for a massively inflated amount. Without that profit it's not worth it. For a normal person, being able to make money on the deal is nice, but at least recouping your costs can keep you economically stable and allow you to move on with your life.

I also think that you would want to combine this with some plan for helping low income buyers with the restoration of neglected properties that would normally be snatched up by flippers.

I also think the arbitrary age restriction on owning a rental property needs an exemption for inherited properties if nothing else. A 20ish year old who inherits a home or rental property when their parent(s) die is not abusing a loophole, and immediately hitting them with additional legal problems and forcing them to sell a house that has a tenant already in there is just unnecessary chaos for everyone involved.

I'm also curious how large apartment complexes fit into this plan. Are they also banned? Do you just need an owner to occupy a (potentially much nicer) apartment in the building? If you can still operate a huge apartment complex, I would expect the market to shift heavily towards those. If you can't well, that raises it's own issues around urban housing and population density.