Please use this thread going forward: [DO] Restaurant: 123:20ece5dd | EA Forums - 11852035
@ToKiHyouI don't know about an "ideal," but logistically, I believe TS4 only allows a total of 20 Sims on one lot unmodded. So counting a minimum of one each chef, waiter, and host, minimum one playable sim, and the unlikely scenario that each dining party consists of only one sim, you should need at MOST 16 seats. Realistically, it's unlikely you'll need even that much, but I find somewhere around that number looks nice aesthetically.
It might be worth fulfilling the minimum number of requirements for the lot and see if that helps, or perhaps swap out the tables and/or chairs used. Maybe also try setting everything (chefs station, host station, wait station, and at least one dining seat) aside in a wide open space to be absolutely sure the game isn't disregarding it due to inaccessibility. You could also try setting it as a generic lot, then saving and replacing it, then set it back to a restaurant.
And if you haven't yet, reinstalling the game could help. If you still use the Origin launcher, you can try right clicking and choosing "repair game" before resorting to an outright reinstall. I'm unsure if the EA launcher has a similar mechanic, though I'd expect it would.
ETA: you don't have to install Better Exceptions if you'd prefer not to, though it doesn't actually affect your game in any way. All it does in intercept when the game throws an error and makes the error file more readable. It could help diagnose the issue, but it's not necessary.
