Once you reach that level, you can either farm a few hundred more company levels (either manually or with a mouse micro), or go for an arduous stock run that will give you a LOT of shares. But either will have little effect, since your decorations should already be pretty high and their effect per level keeps diminishing.

The further progress comes from the store level/store multiplier - so spend all your rubies on it, and try to get all the multipliers you can from special events.

Not that this progress is important for anything. The last reward is being able to reach 15000 in weekly tournaments (this is the last prize level).